ORIGINAL: lukesp
...what Da Rock said.
These launchers really do work well, as long as the catch works freely AND holds the model until you want it released. Make sure of that. I had to play with mine until it did what I wanted it to. BTW, the space on mine where the model's tail loop goes is way too wide, I need to make it narrower. The less distance the pin has to travel the better. I have been meaning to do that for the past ten years.
The one I built was like that too at first. So I put a block in between the two sides that was where the inner side would have to be moved to to narrow the gap. Didn't have to move anything. And the filler block is under no load. All it has to do is make where the tail loop goes less wide. Took no time at all to do. And the launches got instantly better.