You can go for a Superchip mate as these are most common etc.

I had one on my S2 but also had to buy a -31 act and an uprated
fuel pump as my pne died on the rolling road

All in all its how much you have to spend really as now i would not
bother with it and go straight for a complete engine management
system like gotech from jamsport.

I think i paid nearly £750 all in when i got mine chipped and they are
banging out Gotech for £1000+vat makes sense if you know what i
mean.

Phhheeeeewww sorry for the long reply mate