Just a minor correction......
The 'on condition' inspection (including the compression check) has to be carried every 100 hrs or annually, whichever occurs first.
It is all detailed in CAA Airworthiness Notice 35.
One point to note, the cylinder compression check is done with the piston at top dead centre so it will only tell you how the valves and rings are seating, not whether the cylinder itself has a crack in it.
In my experience, total achieved life has more to do with regular, careful useage than living indoors.
As for the Hewland engine, by far the best option would be to contact other operators and see what their experiences are.