With a plate diff, you need to maintain it regularly. The Plates need renewing, timescale according to use. Not really viable, unless pockets are very deep. I was told they are a lot harsher in operation too.
....According what Wavetrac manufacturer Autotech say on VWvotex forum:
"You will not need to change the friction plates. The friction plates will last a very very long time. If it does wear, it will not affect the performance of the differential as it will still create friction againts the house like a standard torque biasing differential. The real improvement is the "wave" gear in the differential which creates a no-load biasing ratio."So perhaps the need to renew plates is no longer a consideration, but Jonny's experience suggests that they are not best used in a road car, even a very fast road car. The young Yankee dudes with their highly modded GTI's won't be phased though!
The Quaife ATB version is surprisingly (to me) smooooth, regardless of the host car's power. The VWR 330bhp Red Temptress is totally comfortable with the Quaife. In fact I'm sure she'd be much more of a handful without it!
Okay, I'm singing the Quaife's praises without the personal experience of other alternatives, but it's not very difficult to see how well and smoothly it performs on a fast FWD road car. You don't notice it's there unless you are both 'making progress' and focussed on your driving and valuable feedback from the car.
I think it was you, Dave, and also implied by Jonny in this thread, that it's the driver rather than the car which has limits (Mark at VWR has also said this) and it's safer to have a car which can perform beyond your limits - Providing of course that you also apply the addage of "With Power Comes Responsibility". I hope I'm making sense as I just spill these thoughts out.
I've said it before and I still think it's true that every FWD car of 2.0litres and more, really needs a diff - Even VW acknowledge this by their addition of their electronic diff on the Mk6, and Renault, and the new Ford RS with an ATB Quaife.