I have a ZDZ 40cc with the rotary rear valve intake. I think you're right about the ZDZ's. It's one reason they tend to be slightly more expensive.

However, it's a dawg compared to say an OS 33, DLE35 or even a PTE36, all reed valve engines. The rotary valve requires proper running in to fully seat, over many runs. Point is that the humble and simple reed valve enables an engine to run at it's best straight from the box and that's been proven with at least half dozen engine makes.

But it has it's limitations as Aviator, Truckracer and Wy8e have already stated. All engines I've played with were operated at less than 10K, in the wheel house for reeds

Wy8e, curious about what porting is in a racing boat engine....These guys operate at 15K +