Its a good little engine, and runs/idles well, is reliable and uses barely any fuel, I dont own one but have seen two run at the field. Downside is as you say at 15cc it is at the point where it is a bit heavy compared to glow power and it is not the strongest engine out there. For the right airframes where power to weight is not everythingand have enough wing to take the extra loadingit would be perfect.

If you have not bought a airframe yet and want to go gas I would skip the 15cc size and go straight to the 20 size engines, rcgf 20 or dle 20, and fit them in90 size airframesyou wont look back. Bags of power.