Ok, I almost meet all your qualifications. The one I don't meet is being the actual owner of the engine but I have helped a few guys that do own the engines get them tuned and flying.

My opinion?
Excellent engines for the price.

Pluses -
Once tuned, good power curves, good overall power.
Common mounting dimensions to other engines Including for exhausts etc.
Decent power to weight.
Parts are interchangeable with a couple of other brands (who cares - this is how business works in China and it sure helps for parts availability)
Low price.
Same "industry standard" ignitions and carbs as many other brands use.

Minuses -
The same Chinese bearings as most Chinese engines use (Chinese supplied NSK's are not really supplied from Japan as many of the makers over there will have you believe). These can be hit or miss but if they fail, they fail very early in the peace - like most chinese engines. - Replacement cost is very low for decent off the shelf bearings. The failure rate of these is no higher than the other brands that use them.
Cylinders can be anywhere between round or not round (Turned internals that are simply flash chromed by flame hardening and no final finishing for roundness or taper - just like pretty much every other chinese engine)
Cylinder rings are hard and take a while to run in - easy fix - Frank Bowman rings are low cost and very good.

General
Once tuned and run in - good value for money.
Wont last as long as a more expensive top end engine so the price per flying hour is probably a little more however the Capital expenditure up front is less. Many people throw their low cost engines out regularly anyway.

You get what you pay for, expect to perform some maintenance earlier than you would with the more expensive brands (such as bearing replacements and crankcase sealing - very easy tasks to perform.)