I'll throw in my 2 cents here..

I started learning with a Sterling Fledgling and an OS FS-40
I never crashed that plane during training..
It kept going for 2 years until the wing bolt mount failed in flight followed by a quick trip to the round.

The FS-40 survived that crash and is powering my step sons Eagle II today.. Still going strong.

Why do I like a 4 stroke on a trainer?
They swing a big prop so you get better prop braking.
Good power but not screaming fast..
It's quiet and souls cool

I've have 3 - 4 strokes (FS-40 FS-61 and a Saito FA-45) I got 20 years ago.
All of em are still running great.. I don't find them any harder to keep running than the 2 strokes.

The biggest problem I see at the field is people running the 4 strokes to lean or at RPM's highr than the motor can handle.
You can't tune it like a 2 cycle motor.

It's not harder.. Just different.

Fact is I have more trouble with the OS .45 FSR than any of my 4 strokes.

The downside is cost weight and future use.. A little 4 stroke will cost you as much as a ST3500..
They weight is a bit more than a 2 stroke of equal size.
I'm kinda stumped for a plane to use it on after the kid is finished with the Eagle.

It would be great in a twin but then I'd need to find another one.