I fly an EA81 with a belt redrive, and am getting comments from pilot passengers that it is the smoothest, quietest engine they have ever flown behind, despite being hung on fairly stiff urethane bushes in an all-metal aircraft.
The main penalty, when compared with a 912, is approx 25 kilos extra to carry by the time you add radiator and coolant (although my radiator is clearly bigger than it needs to be)
The biggest plus is the cost, or lack of! I had 2 engines given to me, and picked up a third for $40 out of the local paper. A full rebuild kit - pistons, rings, gudgeons, small end bushes, main and big end bearings, all gaskets and seals costs $420.00 from SupaCheap, and thats for an Australian ACL package. Add about $60 each for a new water pump and oil pump and you have a zero time engine for under $600
The other plus is that EA81's simply don't break - they are bulletproof