Thank you for your thoughts SF.
The maintenance aspects I had not considered, the 7kg of additional weight I viewed as being offset by not needing to carry as much fuel. Rotax are claiming 20 - 30% less fuel burn.
The reliability of the 912 iS design is of concern at this early stage in its life with little history.
The 912 iS is claimed to be much smoother running with lower vibration.
The drawbacks of the 912 ULS as I understand it are:
Carb rubber mounting splitting
Carb balancing issues
Having only operated Lycomings in the past I only have Internet information relating to the Rotax engines.
NTB