I personally love them. I see them as a super heavy plank
A friend of mine that I help with his training has done in the high 600 (might be over 700 now) on this (he can full Zercher squat 500, which is more than he can front and back squat). The dude is a beat. 6’5", 275 freaking lean (I’m talking photoshoot lean without effort) and his trunk/core in unbreakable.