Quaife atb fitted and gave it some abuse at Harewood last weekend (eventually).

Completely different technique required - Turn in at usual speed, then floor it and hang on, oh and don't lift or you'll get shitloads of understeer.

More understeer in the wet/damp than an open diff as well.

Zero understeer mid corner to exit on full throttle.

Bought from QK performance for £622 delivered.
Quaife quoting around £650

Can't recommend a diff enough. The st170 was spinning the inside wheel on the exit of every corner, wasting what power there is and chewing the tyres up.

Useful on the road, but you have to commit to the throttle early in the corner to get the best out of it.