It's kind of difficult to really figure out what the important changes are - I actually own a copy of eComStation, but I'm not really an OS2 expert, nor do I really know what the pressing faults were with version 2.0 that needed fixing with version 2.1. I do understand a few, such as AHCI support and the updated boot logo and wallpapers (no, really?). Another change which is obviously quite important is AiR-Boot, a small x86 bootloader which resides entirely in track 0 of the hard drive and is operating system-independent. This allows eCS to be installed on Windows 7 systems.
eComStation comes in three versions, namely Home & Student, Business Edition, and Server Edition. The Home & Student version can be installed on one machine, while the Business edition allows for up to five installations. The Server Edition adds the IBM Warp Server for eBusiness components so you can setup a server environment.
You can buy eComStation 2.1 via any of the listed resellers.