Hi Gary - I've got Revo Stage1 (and lots of hardware mods which contribute to performance when remapped). The Revo guys are excellent and well established.
Go for the standard Revo Stage1 switch box to start off with and see how you like it. You can pay an extra £50 when you want a Stage2. It doesn't make great sense to have a Stage2 without having the other mods. But beware coz modding is a very slippery slope and not cheap yet for Mk5's.
I've done 44,000 miles including limitless German autobahns and other parts of Europe and am satisfied with Stage1.