Issues
As said above Thielert have had some issues and they have gone a long way to fixing them on the 2.0L engine (one of the bigest problems with the engine was due to the heat exchangers that Diamond fitted in the airframes).
On the whole The Thielert engine has had a lot of improvment due feedback from it's instalation in military drones, the hours flown by the military are far greater than any civilian use, this feedback can only be good for the civilan users in the long run.
Diamond are now fitting the Austro engine, this has a steel crank case and so weighs more than the Thielert, I suspect that the extra power of the Austro is countered by the extra weight and so users will see no more performance it the aircraft.