You might consider posting on audizine, it's a much more active board.
In short, MTM/ABT/Revo/GIAC/APR/Stasis all have their own stats, but they're close.
There are warranty issues involved. Audi recently released a statement to dealers about it, but some dealers remain pretty open to it. I've not read of many chipped owners having extra problems, as the engine is definitely solid enough to handle more power.
Stasis charges more than the others, but will take care of issues that come up that aren't covered by Audi's warranty.



(google "TD1 audi")
