I just had one of the no-name rectangular ones fail on me. It was the kind with the clear housing so I could see there was plenty of fuel in it. But no fuel came out when I pressed the button. It was usable as a spark wheel only. I didn't see any visible clogging in the nozzle and I've since thrown it away. The thing was, I dunno, at least 3 years old and I'd tested it a few times over that period and it had always worked, but I had occasion to use it a couple weeks ago, and dug it out with the above results. The spark it made was actually enough for my purpose though (lighting a gas stove).