I suppose it's only fair that I should also throw out my biggest CON: It makes no sense to buy such an expensive engine with the intent of only using it in ONE model. You'd just HAVE to imagine putting in into several different models over time. But that sort of presupposes that the model isn't going to last very long and then you could just take the engine out and mount it in the "new" model. This is the sort of thinking I had back when I first started the RC hobby and thought I could get away with only one engine and only one flight pack. I never imagined I have more than one RC model...at a time!
And we all know how that works out. I think my current count is 3 x Saito 56, 1 Saito 72, 1 Saito 82, 1 RCV 91cd and a couple of now no longer functioning (I think) Magnum 52s and that original Magnum 2 stroke I used on my trainer, i.e. the "only engine" I thought I'd ever own.
Most are currently already in a model.
Strangely "the sound" is not such a big deal for me. Both Gas engines and 4-strokes sound pretty good. And once it's up there in the air on the far side of the flying field you can't hear much anyway, particularly if you're flying the thing a 1/4 throttle. I don't really care much what it sounds like on the ground.