I have built several Nitro Plane models. As with many Chinese ARFs these days, They have there issues, but........... They do have a support thread on RCU (never had to use it), and the prices are very reasonable as you have seen.
Now, as for the planes, yes, the manuals are almost worthless, yet I have gotten some control throw and CG info from them that was helpful. Their covering is not crap IMO, in general. As he said, there may be exceptions, but the ones I have built were good. Actually, less than the normal re shrinking, on mine anyway. The material can be fixed with covering my local HS usually has. I always seal all the edges down on any ARF I build, whatever the brand. So continual gluing I just don't have to do, on any ARF. The airframes are well designed with interlocking parts that are laser cut as with any ARF these days. The fiberglass parts fit well and the paint matches the covering. Clear parts like canopies are as good as anybody elses. And if they need paint on them, they are painted. Most hardware IS crap, but that is almost a trademark of these inexpensive imports. Just replace the stuff you need to. No big deal to me.
I know guys that use the oem stuff and have no problems. They are equipped with CA hinges. I have used them and not used them and either way had no problems. I always seal all the surface gaps with clear Ultracote anyway. Add some support or glue to the gear mounts and fire wall as with any ARF.
As with any airplane, if you intend to overpower it, as many of us do, take a look at beefing up what you need to or you will likely be disappointed.
Conclusion, If you see something you like, and you know your way around an airplane, and are willing to do what it takes to do it right without cutting corners, then you will save some money with their planes and have a good flyer.
Happy landings
.
P.S. The P-38 in my avitar is one of theirs. I did a lot of work to it to make it more scale, but at 90" it was the best plane of its size out there as a place to start for my project, and it was but a fraction in cost of the competition. It looks great, and it is among the best flying P-38s out there at any price. I had two engine failures early on, one about 8 minutes in on the maiden no less, and the second right after take off, and both times I brought her home safely on one engine. This is one great flying P-38.