[rwalker]

I have a Quaife from HP Autosport. I ordered it right before the M Perf diff became available.

The good: the Quaife works really well to put the power down without taxing the rear brakes (e-diff stays enabled, but can remain mostly inactive). Yes, I notice the LSD on the street because I'm JB4+FBO+100oct and like corners. I think it's a must-have for autox and track days. There is zero noise (unlike the WaveTrac in my e90, which had a slight whine at highway cruise). The Quaife was cheaper than M Perf parts-wise. Harold gave me a break for being an early adopter and because we had a few delays.

The not as good: installation turned out to be a lot more expensive than the M Perf, dealer installed option. Also, I get no credit for it in lease return, so I kept my stock pumpkin.

I don't regret paying a bit more. I've heard nightmares about clutch type diffs wearing out after a couple of track days whereas the Quaife should outlast the car. YMMV.