Made my own tensioner. Seems to work.
The one that comes with all kits is a POS, but everyone already knows that. It does not matter if you screw the bracket to the frame or not, the fact is the bracket and the steel that it is made of are made in a Chinese prison...you can't reinforce bad quality and design. If you have a "stock" tensioner eventually it will fly into your spokes, hopefully you are going slow when it happens...
I made it using 2 "U" clamps, bolts and some pre-cut steel from Home Depot. Takes some tinkering to get the chain alignment just right, but this one will not fly into your spokes.
Email me at firstname.lastname@example.org
and I will email you a pic...I can't get it to upload here....it is worth trying, I made one for each of my bikes and after about 100 miles each they both work and are cheap and easy to make!