Guy here, I've worn a few in my time and it's a lot like wearing a new ring on your finger, at first you notice it constantly, you feel it between your fingers and you notice when it moves, but eventually you forget it's even there. Exact same experience with thongs. After the initial sensory experience wears off its as present in your mind as the underwear you're currently wearing. It doesn't move much between the cheeks, and I can't say I've ever explicitly felt it shading my asshole.
Personally I'm not a fan of them because they don't provide the two things I wear underwear for, padding between my thighs so they don't chafe, and decency if I manage to cut it rip my pants while working. If I don't need to worry about those I'll just go commando.