I fitted my Gtech 1 myself with the easy to follow guide that I got off graham,L.
I was running my coupe with no other mods but a K&N 57i kit and most importantly a boost gauge. i suspect the chip had increased performance by another 30bhp max. taking me to maybe 250bhp on a cold day, letting the boost spike to 1.2bar. This is pretty much as far as you can go though, anymore and your intercooler will struggle to keep induction temps down. I fitted a boost valve to turn down the boost on hot days. The Gtech is a plug n play chip. It should be fitted with a boost gauge although this is true of all chips. For reassurance after fitting get the car rolling roaded to check fueling.
It would be unwise to run more than 250bhp on a stock intercooler. Infact on a hot day this is pretty much borderline. The only bad bit about any chip is it will put more stain on a heavily worn clutch and the same is so of the Turbo.
Short of it is the extra 30bhp takes a healthy engine close to its limit if on stock cooling. If your engine is unhealthy, clutch worn, turbo seals worn then you will have a few big bills coming that bit faster.