I've used all 20 patches in this kit, and the key is that they don't work unless you prepare the area carefully, and the hole isn't next to a 'ridge' in the tire.  Bike inner tubes have a fine ridge that usually goes down the center of the tire, which is left-over from the molding process.  This ridge can create a pocket under these glueless patches and allow air to escape, since there is no rubber glue to fill the gap. Out of the 20 patches in this kit, I think about 3 failed because the hole was so near to one of the ridges on the inner tube that I couldn't get the patch to rest flat against the tire.  Later on I realized that you can still use these patches near ridges, but you have to use the buffer tool to grind away the rubber of the ridge so it's very flat, and then the patch will hold.  I also pre-stretch the rubber a bit by applying the patch when the tube is partially inflated, and then press down hard - basically grinding the patch into the surface of the tire like someone trying to squish a bug that they absolutely hate.