These work ok.
Here is what I do when I run a frame without integrated chain tensioners:
1) Grab a scrap sheet of a material like plywood, polypropylene, nylon, etc., of the same thickness as your dropouts
2) Cut a 10/14 mm wide strip.
3) Cut 2 pieces of that strip that are slightly longer than the gap between your axle and the front end of your dropouts. If the gap to make the chain tight is 20 mm, then cut at least 23 mm.
4) File/grind the strips to the shape like this: (------( where "-" stands for the material. Basically, you just create a shape that looks like the tensioners above but with an open axle hole.
5) File the strips to the exact length
Quick, cheap and reliable solution for a tight chain!