Their own design, from a few years ago, is better and was a 4 cyl 2 stroke, with an electricaly augmented turbocharger.
The SMA 4 stroke is to heavy and produces high torque pulses that hammer the prop.
I would not touch it with a barge poll.
TCM have been in the engine business to long to believe in new designs.
2 stroke diesels are a better way to go.
See this from Ecomotors, an opposed piston engine with a single crankshaft and an electrically augmented turbocharger.
Advanced Propulsion Technologies, Inc.
Good power to weight ratio, simple design and with very low vibration.
Eurocopters are investigating using them in future machines.