I don’t know if it counts as a controller per se, but I’ve been using an MMO mouse with a big number pad for the thumb for quite a few years now. I used to laugh at these things, but once I tried one, I couldn’t go back. Those extra buttons come in handy a lot more often than you might think, and sometimes I wish it had even more.
If you have any interest at all in Souls-likes and want to see where the genre really started, consider Blade of Darkness. An updated version is available on GOG with modern resolution support and slightly improved controls (still clunky as hell in comparison to newer games, though).