On the mk6's, mechatronics issues were very rare.
http://www.golfmk6.com/forums/showthread.php?t=14811
I believe it was more of an issue on the mk5's. It's an expensive part to fix (couple thousand to replace), but should be covered by the 5yr / 60k powertrain warranty. When you go for a test-drive, make sure to pay attention to the transmission in 1st. If the car hesitates moving from a stop, then you hear a loud bang and feel like you got rear-ended, you know the mechatronics unit is going bad.