Biggest hunk of junk, the MDS 58. Flip side of that, I have the MDS 68 and it is still A runner. If they would have just figured out how to make A carb the rest of the engine was good. I sent the 58 back because of bad running and breakage and I have the third one in A box. Can get it to bench run but in A plane it stinks.
I have two LA 46s, perfect right out of the box and can't tell you how many gallons of fuel have gone through them. These are in light fun fly planes and have plenty of power for there use, not for racing though.
In four strokes I have had great luck with the OS, I have three, 2 120s and A 70 but I think the Saitos are more user friendly, JMO. My YS is A mite touchy after I messed it up with dirt and ground contact, I just got it back from being rebuilt and it is still broken, going back to YS Monday, there service dept. missed something in the pump, they didn't bench run it.
I'm now going to stick with gas engines, I love my RCS 1.40 and have never seen A problem with A Zin, the next engine is going to be another gas in the 45 to 65 range, at this time???? Not sure of the plane yet either.