diesels are so damn compatible with forced induction (turbo's)... i wish petrol's were like that...
Tudu - i know you only gained ~10 bhp for £300, but i myself have seen what these people do when they are remapping (changing the fuel-air mixture etc) and when they quote 25bhp, it isn't really true IMMEDIATELY but after a few thousand miles its meant to 'set in', and even then, it wont reach 25bhp, more like 15-18max. But in my personal opinion 10bhp for £300 for a petrol engine is good 'bang for ur buck', since if u think about it, exhaust systems and all that cost around £500 (typically) and they only give gains of 10-15bhp in reality.
Its just a nice quick increase in power, without having to do heavy modifications to the engine.