Unlike everyone else, i actually run one of these Racingdiffs progressive LSD's on my track car and i can tell you it works. I can't compare it to a factory LSD as I've never driven one, but certainly going from an open center, to a welded diff, to the above progressive LSD, it defintely works.
I'll try to do a breakaway torque test of my diff over the coming weeks and will report back with the results.
For reference, I'm from Aus and drive a 93 E36 325i (almost finished my turbo build). You can check out some of my racing with the welded diff and LSD on my youtube channel too: https://www.youtube.com/user/dominator293