I'm an avowed Protonaut.
I consider it to be a "sleeper" brand because it's top-shelf functionality and quality, but doesn't win the chrome beauty-queen awards, and doesn't get advertised to consumers. People who don't know tools, sell it for cheap because it isn't one of the heavily advertised brands. People who do know tools, generally ask fancy prices for Proto because of its reputation and generally good warranty. In that respect, Proto is a bellweather tool for discerning seller sophistication!
Proto also has a very proud history. It was Proto tools (well, it was called Plomb, back then) that made the largest contribution to the WWII war effort. You can trace the Proto heritage all the way back to 1907 and a couple of German immigrants who started forging tools out of model T axles in a small shop in Los Angeles.
Proto watchers were/are nervous about the Stanley takeover in 1984, but most reports are that the quality has not suffered that much, if at all, so far (debatable of course). Still a proud made-in-USA brand (not sure if that can be said about EVERY tool, but most)...keeping our fingers crossed.