The ability to find replacement parts is key, so good job over_stock contacting Sun Sun.
I think a direct side by side comparison of the Marineland and the Sun Sun would be very beneficial. Some of the issues I'm seeing here may be design issues, not build issues. Since the design is practically, or exactly, the same as the Marineland, any design issues can't be attributed to the "cheap knock-off" argument.
Build issues, such as cheaper materials (i.e. thinner plastic, flimsier o-rings, etc.) and quality issues can be attributed to the "knock-off" argument.
The two big questions I'd like to have answered(and only time will tell) are:
1) Pump reliability...how long will it last?
2)For the UV models, is the plastic that is exposed to the UV shielded? If not, that's gonna be an issue sooner than later.
I think the one other issue here could be quality, and I mean in the manufacturing sense. Will every unit produced be as good as every other unit produced, or will there be duds, and if so what percentage. With Eheims, Renas, Fluvals, etc. quality is key. Yes there is the occasional lemon, but they seek to minimize it. I think the issue with a lot of the Chinese products is that they don't seek to minimize the number of lemons...they just ship them/sell them anyway.