Phiippa,
First off, after I post this message, I'll be moving this thread to the JFBConnect Pre-Sales area. Somehow, this ended up in the wrong section, so I wanted you to know where to look.
As for your question, JFBConnect completes 100% standard Joomla users, which any other component will work just fine with. While we don't test directly with RedShop, we've heard of other users who have them both without issue. With that said, we don't have a "Profile plugin" for RedShop, which means that you won't be able to import the user's Facebook profile information into RedShop directly. However, the quicker registration process through Facebook, the Like, comments and other social widgets, Page Tab integration, Requests, and all other features should work just fine with RedShop, and just about any other component.
Hope that helps explain, but if you have other questions, just let us know!
Alex