The Haldex unit controller only applies to cars equipped with Haldex. For Audi, it would be the TT and A3 (R32 for VW). Rest of Audi have the torsen system. With the controller, you can switch into 3 different modes were in race mode, you will transfer a max of 75% to the rear. The unit will also make the engagement sooner especially on heavy acceleration. As far as stress goes, there are plenty of MarkIV R32s with the controller and they have been heavily modded. (vortex R32 mark IV forum has a lot of them) Just like any mod, it will put more "stress" due to more usage of certain parts;but haven't seen any complaints or bad review so far.