For future reference, a similar mod that works is:
https://te4.org/games/addons/tome/sk_rae__arendeth_fork_multi_class_challenge
Put the .teaa file in the addons folder under steamapps/common/TalesMajEyal

Unfortunately same as below

Hi there. Just wanted to report that I ran into a problem with this mod on the latest version of the game. Only running the stock content pack plus the official DLCs, and when I click on the DualClass tab under Game Options, I get an error. It's longish so I won't post it here, but it should be readily reproducible. Says there was an "attempt to perform arithmetic on field 'default_random_rare_chance', a nil value". Happens repeatedly and doesn't affect game stability, but it does render the mod unusable.

Hi what's the difference between this and the forks on the tome website

So, I have managed to solve both issues. I commented out the "local Object = require "mod.class.Object"" line in the load.lua file and suddenly it's working well with Cleaner Item Descriptions and Command Staff suddenly works again. I have no idea WHY that line would cause those problems, and I might have broken something else, but it seems to run just fine now.

I think this mod also makes it so the only eligible element for staves is physical, making all staves do physical damage and breaking the Command Staff talent.

Same thing with Cleaner Item Descriptions

This mod seems to be incompatible with Better Item Descriptions (it crashes on startup with both mods).