I have run the Magnum .52 XLS, The ASP .52 ( New series = same as Magnum), and the Tiger Shark .52 and .56. They are all great engines. The low end needle valve on the Magnum/ASP has to be in a lot more than factory recommendations (approx 1 turn out from fully closed) to get the transition smooth, but once it is set the transition is as smooth as any OS I have dealt with. Reliability has been great for all of these, (except the Tiger Shark .56, which is working great but I have not had it for long so I cannot really comment on long term reliability - I guess it will be fine as well over the long run). The Tiger Shark .56 is a REAL POWERHOUSE, I think it will be one of my favorites for the future. All these mentioned engines comfortably outperform the OS .46 FX, my trusty old benchmark engine. I have also had good luck with GMS engines, and so has my friends, but have read some bad comments about them. Maybe there was a bad batch at one time. I have one in a float plane that has NEVER given me a deadstick.