What is it ?

A mod adding a new weapon : the musket , the closest we might get to a vanilla-ish pistol in modded minecraft. It also adds a new gunslinger illager, which wield this weapon in outposts and he rarely appears during raids (similar to evoker spawn chance).

What does it offer ?

A new craftable range weapon with its own selection of enchantments (as well as some cartridge variety ) and tons of compatibilities with other mods.
The Gunslinger's AI is pretty basic, but still better than vanilla pillagers as it actually tries to use some hit and run strategy, which works quite well in raids. He also looks good (doesn't have much in terms of unique sounds though).

Cons :
The weapon is not that easy to use, and by that I mean it's quite hard to tell if you'll actually hit your target. More than once I managed to hurt enemies in fights by not actually taking the time to aim properly, so for a regular player it would seems more useful to use in closer range and with little aiming.
I would recommend increasing the base damage of the gun as since its hard to aim you might as well make it stronger, that said you can sort of do that in the configs already. Also the Gunslinger illager has quite the good aim, maybe a bit too good, making raids harder (that said he doesn't appear in big numbers, but note that having this mod installed means raid will become a bit more of a late game thing). I would also like it more if you were able to properly configure the exact amount of gunslinger illagers in each wave.

In conclusion

Even though I quite like the mod, its flaws prevent me from giving it the best of ratings, plus there is plenty of similar gun mods out there which add more content than this one. But yeah it's a pretty average mod overall and has its uses in survival modpacks too.