Well, the heat type patches are truly permanent. The heat vulcanizes the patch to the tube. Adhesive patches, whether pre-glued ("glueless") or traditional glue on, rely on the adhesive to hold the patch in place. When they were first introduced, they had a pretty high failure rate. They were improved pretty quickly, though. In a car or truck tire, the tire is heated enough to cause the patch to vulcanize to the tire. That doesn't happen in a bike tire (good thing, or your tube would vulcanize itself to the tire, which does happen in tube type tires on cars sometimes.), so if you attack the patch's glue with the right solvent, you can undo it, much later.

I haven't had much luck with glueless patches, but I've only used them on the side of the road, and i've not had much luck with any patch on the side of the road.