To the best of my knowledge, FB for Sense will allow the Friendstream app and widget "understand" you are signed in. Facebook for Android will not. It works the same with Twitter and Twitter for Sense. Only need to use the for Sense version if you want to use Friendstream.
The one thing I noticed was if you go to your gallery and try to upload pictures to fb, the Reg one only allows you to upload one pic at a time. The fb sense will able you to select multiple pic's at one time.
As stated above Facebook for HTC Sense (and the Twitter equivalent) are asically hooks for Friend-stream (and the HTC Twitter widget), but they are NOT full fledged apps.