What is it ?

This is a mod which adds a custom system of qualities to almost every type of tools, weapons and armor, which is compatible with bauble-slot items too.
This basically means that every item crafted, traded or simply found will now have a chance to get a randomly-assignated quality upon player obtention.
It is of note that this mod depends on potioncore, which means it also uses potioncore's custom attributes in order to add more interesting qualities to items.

What does it offer ?

Randomly-selected qualities on certain items obtained in the game, which might increase or decrease certains stats about said items,
making every item feel a bit more unique outside of enchantments.
The custom emerald ring and amulet automatically become baubles-wearable if it is present, which could serve as some example equipement to test custom configurations for these slots in your modpack.
It also adds a reforging station, which you can use in some cases to try your luck again with the qualities at the cost of a material tied to the tool (think of it as using iron on an anvil to repair your iron sword, its pretty similar here).

This mod however has some performance issues, as for some reason it makes your game lag regularly even when only it and potioncore are loaded, and I also don't really like how the only way for modded items to receive a change in their quality by default is more often than not to get your hands on several nether stars and hope you'll get lucky with the rolls as it can become worse than what it originally was (at least you can configure custom materials for specific tools yourself, I would have ranked it even lower if it didn't).
Some way of knowing the quality of an item after it has been randomly selected without having to select it with your mouse would have been nice too, but I guess that's a bit more a matter of personal taste and preferences here.

In conclusion

I quite like the concept of this mod, as adding randomly generated and easily configurable stats to items allows for more variety which could be a great addition to a more roguelike/dungeon crawling type modpack for example, but I think that this unfortunate negative impact it has on the default game's performances makes it hardly usable for most modpacks out there, I myself had to remove it from some packs I was working on due to this.

I would also like to mention for people looking for a port/fork of this mod or at least a maintained version that Quality Equipment exists on more recent versions of the game, and it's basically the same thing (I learned about this mod while writing this review).