I actually can't really point out anything as dumb as it sounds. I dislike the config and i dislike the way some commands behave, thats pretty much it tho
A better alternative for EssentialsX, allowing you to use vanilla selectors like @e, @a, or @s. Bookshelf also offers a powerful API that can be used for everyday plugin development.
CMI is heavy but the features are much more complete. I swapped early on and never regretted it. CMI took over for half a dozen premium plugins I was going to have to buy.
Essentials Kits don't even save NBT data, or they didn't the last time I had used it. CMI handles my rotating message scheduling, portals for executing commands on area entry, Holograms, command aliasing, full rank handler, chat filtering, allows commands to be run on offline users, Ender viewing and editing as seperate features. It has significantly more features, and more of them being complete. Essentials did maybe 5% of what CMI now does for my server. Half the time I look for a new plugin to implement a feature, it turns out CMI already had a module for it.
For my server I wanted to implement MCMMO levels as a requirement for ranks, which CMI did out of the box. Essentials I don't believe had that feature when I looked.
essentials isnt perfect noone says that, but its also free, hasnt had the exploits cmi had, and the free standalone plugins for those features are better than cmi