It depends on the generation of the engine.
The older generations had some problems that were corrected by Thielert replacing the engine block - all new engine designs have bugs and that is why I would be really concerned about the many 1st generation engines from little companies that don't get longer than that in generations. On the newest generation Centurion 1.7 engine our flying club has had not. The diesel Cessna 172 in our flying club is used for training, the Diamond however, is not used for training - what challenges the new pilots then would have if they would fly the very easy plane from the beginning
The yearly collected number of hours for the C172 is pretty high and the support from Thielert has been so far excellent.
Despite if you would face some problems, Thielert is a rare company that will come and replace the engine for you. And the auto conversion Centurion 1.7 is no longer available
and Thielert is selling only the 2.0 that has their own engine block which hopefully is free of these problems.
Isn't it nice if you can all the time fly with a new engine at Thielert's expense? In that light, I wouldn't hesitate installing it on experimental aircraft,
provided the support would be equal. However, it is not equal and the engines aren't sold for experimental aircraft however.
I think Thielert is one of the rare engine companies that can solve the challenging issues there are always in new engine development.
I would bet that eventually is will become a new Lycoming - a new de-facto standard everybody uses. Gasoline engines are really at the end of their
life, the market is small and there is no room for too many different big companies, and I am pretty confident that Thielert will be there, so
IMHO Thielert has the most ingredients for that of all the companies making new engine development currently.