Ive never seen people use it but imo outs pretty decent on a wall or something. Why does nobody use it or is it cuz its nit very well known
Ptetty much generally across gen 8 formats
They are useful but niche.
Kee berries raise defence. bulky Pokemon like to have leftovers. They can have defence evs instead even +defence nature. It's still recommended for some mons though. It's a good item as nothing like assault vest counter part exists yet. Here
maranga berry is even more niche. why not assault vest instead? it's for whole battle until knocked off just like maranga berry can be knocked off. But walls can use this becoz they need status moves! Regardless it's also recommended for few mons. Here
Overall they are good items. You can certainly use them if you like. I personally use kee berry on volcarona in gen 7 ou. It works pretty well.
Hope I Helped!