It's very easy to remove that DRM. Personally I don't log in to my kobo so library books get stripped before being copied over (the kobo acts as a usb storage device).
The most recent version of DRM used by Amazon hasn't been cracked yet (AFAIK) and the workarounds get you a version of the file missing a lot of recent typographic improvements.
Interesting. I didn't realize they had their own. Thanks.