many on here will remember my 05 plate alhambra tdi 130, a fantastic car all round. however i purchsed what at the time was regarded as the best engine re map available for vw group cars, a dms re map module. the module increased power from 130 bhp to a claimed 172 bhp, i was pleased as punch with the upgrade as it did indeed give much better drivability and around 10 % better fuel economy if driven carefully, if driven hard the fuel consumption was horendous and much worse than the standard cars.
however i soon started to have problems with the dual mass fly wheel and clutch slipping in all gears if i even attempted to get a sprightly get away, having lots of research it soon became apparent that vw group and most other vehickle manufacturers where using duall mass fly wheels now and these items are usually manufactured with just a 5% tolerance of design.
cutting a very long saga short i ended up having a new fly wheel and clutch fitted under warranty (the dms module allowed you to remove the map and wipe the ecu memory so the manufacturer was un aware it had been used) but this too soon started to slip with the re map present, without the re map it was fine.
BUT the final straw came when i was coming home from wales with the van and the engine warning light came on, i called out the rac who told me the engine was over full with oil and they drained some out, this was strange as the car had been dealer serviced and i had checked the oil level prior to setting off. the same thing happened a week later so i took the car back to seat, it turned out the sump was full of diesel, the car had been over fuelling, seat could not understand this as the pump and injector pressures where correct and the compression was perfect of course they knew nothing of the re map. the car was serviced filled with new oil and given back to me along with a quiet word from the mechanic to get rid of it as soon as i could as in his opinion the engine was damaged and would not last long.
i know some have had no problems but do a google search on the subject and you will find that more and more people are realising the mistake of these products, my honest advice having been very lucky to get away with it is, if you need more power buy the next model up, its cheaper in the long run.