I never rode a Stinger kit, but in general the china chains are garbage. Personally I prefer to ride a #41 industrial chain, you can get it at a good hardware store, farm and fleet, or order on Amazon.com etc. I got mine through Amazon from the AceHardware store on there. #41 chain is really solid, you wont break it....
As for the tensioner, I HATED it, after an experience very similar to yours I tossed the kit chain, tossed the tensioner and instelled the #41 chain straight from the motor to the rear sprocket, 2,500+ miles later and not a single problem with the chain! If you do ditch the tensioner I found the easiest way to find the right chain length is to shorten your cheapo chain till it fits without the tensioner (cause they are easier to break and mend), once you have the right length count the links and make a #41 chain with the same number of links. Not EVERY bike can be run without the tensioner, on some bikes the chain will hit the frame if run straight front to back. If you have a clear shot for the chain to run without the tensioner I would highly recomend it, the noise and resistance when pedaling is greatly reduced and so are chain failures.