Wow, now this is telling it like you see it. There are going to be some feelings hurt with this post, but I am glad you didn't hold back and let your thoughts be known. This post here is what this thread is supposed to be all about. What engines to avoid at all cost? Great Post!
ORIGINAL: Cheech
Don't buy MDS. Stands for "Many Deads Sticks" and it's true. Engine is junk.
Don't buy ASP. Not sure if they're sold now, but they are cheap Chinese O/S knockoff garbage. ASP = "Almost Spins Prop". They wear out fast and blow gunk everywhere due to the poor fit.
When you'lre looking for a big engine, don't go buy one of the big Super Tigres. Ditto for the big OS BGX. They're are much better engines out there, like the Moki's.
Why you would ever buy a FOX is beyond me. I ran a Fox .40. Heaviest, lowest power .40 I ever ran.