Had mine done about a month ago...........first impressions it felt no different although the tickover felt alot smoother. But lately the car feels more responsive (could be because ive also changed my fuel from BPultimate to Tesco 99) i would recommend the upgrade to stay in warrenty - but be warned if you have your car chipped because i believe the upgrade erases the chip
....My VW dealer knows about my Revo remap and I switched it to stock for the service. The ECU was updated with 24K6, which they told me solves a few issues of false fault codes. Revo are aware of possible problems if I switch back to Stage1 myself, and so they will sort it out for me - No problem.
Meanwhile I'm running around on stock map and did 409 miles today going to the GTI International show (where I met the famous Teutonic_Tamer - Not especially hairy and a very ince guy). I can only compare with my Revo Stage1, so not relevant to this thread, but such an update won't effect performance - Such updates will merely be fixes.