I have a 90 and one of the guys at our club has the 50. We had a little bit of a fit with a tight carb barrell on the fifty but the co gave us some easy advice on fixxin it and it runs fine now. they have a rep for being slow to break in (most ABCs do). The rep at the co. says they like a slightly longer prop as they are not a high RPM motor. Others I have talked to like 'em my 90 is still in the break in period and is slowly gettin' gooder and gooderererer. I think they are pretty good for the $ but I recomend a good long break in period following the recomended procedure. 1/2 a gallon is a good start. Don't get in a big rush on setting the low end. I think they will last a LONG time if broken in right. Like all ABCs NEVER run em lean and just a LITTLE rich all the time.
One of my Very experienced and trusted flying buds says their 50s are about as powerfull as a good 45 but the price is nicer.