Has anybody tried one of these performance chips that remaps the car giving more power and torque that plugs into the obd plug? [/list]

Yes. Used 2 different boxes, on 2 different cars (both turbo diesel)

On one, it kept logging a fuel temp sensor fault, the other an overboost fault
And that's before we get into the potential pitfalls of overfuelling a diesel engine

Save your money, and get a proper remap

Had Bluefin remap. Loads of black smoke on hard acceleration. But great on power increase and fuel economy though.