I have a 1115GM Changfa from utterpower direct coupled to an ST10kw head. Run standby 50hours. When running at 1800rpm you get about 18HP or so out of it. It likes to run loaded to about 7.5KW (according to my clamp-on ammeter), no smoke, no hard laboring and it seems that's the long-term sweetspot for this setup. Its a serious machine, put it next to a store-brand of the same rated size or even 10-15KW and you see what I mean.
Ok, I understand my experience is just one engine and only 50hrs so for what its worth:
Ready to run out of the box, just add oil and water.
Starts easy. (I use electric start) but it has a decompression lever and crank too.
Western quality. well built. The brand does make a difference IMHO.
Does fine on a trailer, so it can be relocated quickly.
Noisy. It is a large single cylinder thumper. While well balanced and pretty smooth, it still makes a diesel tractor type noise. I think it's a normal sound for a diesel of that size, especially a single cylinder, but don't expect a lister type sound. I will build an enclosure (on the trailer) when time permits, should take the noise down a notch. It also could use a radiator, low oil shutdown and governor adjustment; in other words some convenient refinements.
It runs my whole house, including 2ton central AC unit, no modifications to the engine or generator. I just used them right out of the crate (on purpose just to see how they did) the only thing that happened was a minor fuel leak and the generator bearings need to be repacked.
Solid, kick ass engine and generator for the money. So is the direct-couple from UP. My materials and two days labor built the unit. Another two days to modify a boat trailer and mount it on that. Great project.