I don't know anything about JS Custom Redirect, so I can't really speak to what it does or how we could work together. If it tries to intercept the login process and redirect the user, it will cause problems. If it doesn't trigger during registration, it *may* be ok, but there are things that JFBConnect does after it authenticates a user during the login process which could be problematic if skipped.
I'd contact the JS Custom Redirect developers and see if they have a way to store a bit of data that a user just logged in and then use a system plugin that would trigger on the next page load to actually perform the redirect. That's the recommended way to do things as it doesn't prevent the current login flow from stopping abruptly.
Beyond the above, have you actually tested the above scenario to see if there are problems? Again, I'm going on what you've said of how things work. If things seem to be working properly for authentication and login, then there may not be an issue. Without know the exact details of how the redirection is performed, I'm just guessing.
Thanks,
Alex