Well, as Aramis said, BL is fairly complex - especially the damage system, which is very detailed. Not quite SFB, though - I would say it is roughly equivalent to Classic BattleTech in complexity. If you want battles between starships as tactical games, you should buy it. BL is suitable for battles between ships of up to ~1000 tons - it can handle ships of a few thousand tons, but gets really cumbersome at that point.
BR, on the other hand, is a different beast. It is meant for battles between large combat ships from several thousand tons upwards. The rules are a lot more simple than in BL - no need to record damage on a complex datasheet.
BR is a pure tactical game in itself. You probably won't need it for RPG purposes, but if you enjoy tactical space combat games, you might want to check it out.
Regards,
Tobias
P.S.: Aramis, is your site down? Speaking of ship combat reminded me that you had some MT ship combat stuff I had been meaning to archive...