It's not to much engine for the plane. I had the 50 on the ARF version. I put it in before really getting around to trying to hover it, but during a pull up from a harrier it could easily accelerate vertically. Never had it drop out of a vertical climb...or even slow down for that matter.

I have seen some with the Irvine 53 and also the saito .72, both give better performance than the OS 50, IMO. However, the saito will require taller landing gear. I have a kit in the workshop waiting for space to build, I bought an Irvine 53 for that one.