It has been many years since we dealt with MCMMO, which was an absolute mess of a plugin that didn't play nice with other plugins. Like, it didn't respect worldguard, it did really weird things and cancelled actions by other plugins. It's almost like it was meant to be the ONLY plugin on a server. I recognize the fun things it adds, and I'm perfectly fine with them... it's just a nightmare in many of our memories having to deal with all of the really weird and numerous problems it created.
With that said, if it has been actively and heavily developed for the last several years, then I'm actually not sure what MCMMO is like nowadays. Maybe it's great and compatible with other plugins, I have no idea.