Just bought a mk3
cupra....(3rd 20vt car ive owned) and this
cupra has a greddy one fitted. It only keeps the engine running for 20 secs after turning of car. It does count up if you are on a long distance drive, eg after picking the car up drove the 100mile trip home and the TT wanted to stay on for 8 Mins!
IMO its a waste of money, and what seems like a pain in the a**e to fit, like most people have suggested take it easy towards the end of your journey and let it tick over for 20-30 seconds before switching off.
My TT is perminantly switched off, just doesnt feel right leaving your car with the engine still running.
Save you money and invest in something more worthwhile, of course this is just my opinion. To be fair tho, who ever fitted the TT to my car did a really neat job, so it stays where it is...just switched off