Physically it is small. By comparison to the Logitech or Model M the width is about the same, but the depth is about a third less. It is much lower. There is almost no space around the edge, the keys come right up to it on all sides. It is fairly heavy for its size and seems completely rigid with no trace of flex. It doesn't move at all on the desk. The upper surface is made from a smooth plate of aluminium probably 3mm thick. Underneath, there's a thin layer of smooth and shiny plastic which fits seamlessly. It seems to be screwed on, probably the screws are under small slightly sticky bumps which serve as feet. At the far edge, this plate becomes a raised plastic bar, around 6mm high, which puts the board at a low angle. This bar contains a USB socket in each end, mounted flat. There is no means of adjustment of the desktop angle, which is about the same slope as on the Logitech.
The keys seem to be full size in top area. They are not at all splayed vertically. The result is that the spacing on the backplate is greater than usual - probably 2mm, whereas normally, the bases of the keys almost touch. The keys are very low indeed and the travel is very small, probably about 2mm. The effect of the low travel keys and the heavy backplate is that in use its almost completely silent.
When you decide to use a Mac keyboard you have two choices about key mappings. The first is to arrange the mappings so the keys conform to their labels. This will lead to one kind of irritation. There is no # key label. Keys like `, @ and " are in the "wrong" places. The | key seems to be over on the right, which would be very irritating. These people, you think, must never use pipes or comment their code!
The other thing to do is leave it mapped as a standard 105 key board, and have the letters where your fingers expect them to be, just not as they are labelled. This is the choice I made, only swapping esc and capslock. Its an irritation also, but a minor one.
How does it feel to the fingers to type on for extended periods? It gets cautious approval. The initial impression differs a bit from the impression after a week or two. At first, the effort is quite small, and the amount of movement also very small, but the keys when struck nevertheless give definite positive feedback. You do perhaps notice a tendency to strike them more heavily than one would expect, because there is not, as there is on the old sprung boards, any progressive resistance, so you need to give them a bit of a bang to make sure you trigger them. But this is not heavy by the standards of the old sprung boards, and at first you only just notice it. The same effect on the usual poorly designed OEM keyboards is much more marked and does lead to one banging the keys quite hard, which is tiring and doesn't feel good. Often on these boards you get both mushiness and high effort - the worst of both worlds. This one is very much better than these, it is on the whole low effort and firm.
However, after a week or two, the way the strike does lead to something of a banging action by the fingers becomes more noticeable. It is not very marked, its just that you realize it is less comfortable in extended use than it seemed. The effect is a bit like buying a speaker with over emphasized lower mid range. At first it seems pleasantly warm in tone. After two weeks, you are turning down the bass and wishing you had bought something drier and more neutral. I don't want to make too much of this. Its a factor, its real, but all keyboards have some disadvantage, and this is not at all extreme. However, if you were simply comparing this one with a good buckling spring board, you would probably, at the two or three week mark with that, have stopped noticing the keyboard at all. I don't think, if given the choice purely on the basis of finger feel and typing comfort, and after a longish period of use, that any experienced typist would choose the aluminium one. Which is not to say its bad to type on, it is not, not at all. It's just not at the same level as a sprung one. While it feels different than a good OEM membrane board, because of the low travel, it is probably neither much better nor much worse in terms of the fingers in overall use.
The combination of the angle and the lack of any adjustment is less appealing. It is very low to the desk. The consequence is that with the slight tilt, the hands and fingers are rather awkwardly angled upwards. I don't like this effect at all, it feels as if RSI could be in the offing and as if the tendons on the back of the hand are being perpetually strained. I have tried propping up the front to make it either flat, or tilted down and away from the user, and this is a lot better. It may end up with a couple of small pieces of wood glued on the bottom to remedy it. Some kind of adjustment would improve the thing enormously, but one realizes that however functionally necessary, it would look like unacceptable clutter to Cupertino. With a more conventional keyboard, the angle is about the same, but it seems not to be an issue. It may be to do with the way that the flatness of the Apple keyboard forces a sharper bend upward of the fingers and back of the hand. At least, that's my impression.
What's the bottom line? What should you recommend when people ask? What do you say about it?
The nearest analogy might be the Mac Mini. It is unique in desktop machines: it's the only fully featured machine that you can put in a briefcase or coat pocket or backpack and carry around with you. In exchange for this extreme portability, you make some compromises on price and performance. But if you really need the portability, these will seem very acceptable. There's no other way to get it, and the product itself is well made. If you really need a quality product that is a desktop box that will fit in your pocket, this is what you should buy. Similarly, if you really want a silent keyboard, and if possible a well made one, this is the one to get. You do make some compromises, but there is no other serious contender. This is my own case. I wanted silence, and the compromise in pure typing functionality is real, but small enough to be acceptable if that's what it took to get it.
If silence is not important to you, but writing comfort and ergonomics are, what then? No, in that case you'd probably be better off with something else. Keyboards and screens are probably the two most important aspects of their setup for writers, and probably the three rules are: the screen should be as big as possible, the keyboard must be tried for an extended period at the desk before judging if it's right or not, and the default recommendation is for it to be sprung if that can be afforded.
It is striking that if you ever talk to experienced secretaries of the previous generation about keyboards, they invariably express nostalgia for the 'clickety clack' keyboard. These are also ladies who, despite spending a working life at the keyboard, appear never to have encountered RSI. If your user can afford a sprung keyboard, this is what to recommend. There are degrees of clickety clack -ness. The Model M is at something of an extreme, too clunky for most. The Apple Extended was of the same order, but needs less effort and is less noisy, but it has the same comfortable effect of simply vanishing in use, once you are used to it. The Cherry sprung keyboards have excellent reputations, but I've no personal experience. The Matias uses the same springs as the Extended and has been well reviewed. I have not tried it, but based on the reviews, it can probably be recommended fairly confidently as an Extended equivalent.
If you recommend the original Extended, then you are recommending buying a used board, and matching it with an ADB to DIN converter, and then remapping the key caps. I'm fine doing this for myself, but a bit dubious about it for someone else, who may depend on the machine for his living. However, if they are former Apple users, perhaps upgrading from an old ADB machine, and already have the Extended, its a reasonable choice.
If money is an issue, and with writers it mostly seems to be, I would suggest the Logitech OEM or the similar feeling Microsoft Wired OEM. Its about right in feel, not too mushy, not too much effort, positive action. Yes, you do end up thumping it a bit. Yes, on some keys you may find it hard to get the force exactly right - this happens to me with one or two of the control keys, and so you end up using more pressure than you might like. But they are solidly made, you can get them anywhere, they are quite inexpensive, they are adjustable in height without glueing stuff on the bottom, and their height above the desk, at the front, is going to let you position wrist and hand angles better, more naturally. You can pay a lot more and do a lot worse than with either of these. People who have either of these seem quite happy.
The one I'd most rather use myself, were noise not an issue, is the small sprung one that came with an old SE 30, many years ago. That is compact, high enough off the desk, and has great feel. After many years of use, some of the keys are a bit worn, but it feels as comfortable as ever. On that or indeed on the Extended, I write away without ever thinking about my hands. The only bits of Apple equipment that I'm still using. Which just shows you, perhaps, how personal a matter this is!
Some sources and makes
www.pckeyboards.com (source of Model M equivalents)
http://www.tastaturen.com (source for sprung Cherrys)
http://matias.ca/tactilepro2/ (modern replacement of Extended)
Das Keyboard is a fairly expensive modern sprung entry, well reviewed.
Cherry makes large range of quality keyboards, including sprung.