They can definitely make your favorites cards pop out and provide some UV protection, so Id say its unfair to call them useless/cringe. I have four that i’ve gotten through trades (via “ill throw in the guard if you can do $x”) and I don’t personally use them.
I am paranoid that over time there will be unnecessary pressure applied to the borders of the slab, which might cause frostings and even cracks! If you aren’t careful or have a really cheap guard, your slabs can be chipped which can kill the value of condition rarity cards.
Below is a clip of a E4 member trying to get a shitty temu guard off his card and you can hear an audible crack
