[Lancelot]

Yes, i've got a quaife for my AH3, very happy, and price is similar to the M performance LSD at least in Europe.

You're correct about the different gear ratio, so fitting the m performance LSD would result in higher rpm for same speed/same gear, which can be desirable in some situations, but results in lower fuel economy at least.

I'm not sure what the car ECUs would do with that, perhaps works like a charm (likely - changing final drive ratio is common in racing), perhaps not, but it's expensive to find out...