I recently had a chance to fly behind Thielert's latest version of its 2.0 litre engine, the 2.0s. This is the 155hp engine that Cessna was going to use in the now suspended C172TD. I only got a single flight snapshot, and the engine performed flawlessly throughout, but history shows us that it sometimes takes a little longer, and some fleet hours, before any problems manifest themselves, although it has to be said that the 2.0 engine is slowly building a good reputation, and that the 1.7 litre engine didn't do too badly in individual owner's hands.
Thielert's biggest challenge is now one of reputation. After a bad start this is slowly rebuilding, but aviation is a conservative market and the company will either need lots of time or a buyer with a respected name.