Fullness - way too much if there hasn’t been enough prep (stretching and lubing) or my partner is clueless. It doesn’t feel like a cock or a regular dildo, and I swear I can always feel the knuckles regardless of hand origami.
Most of the time, I don’t particularly enjoy the physical sensation. I would never let a man do it to me as I’d find it way too degrading. I’ve done it with women, but it’s usually been for the benefit of men - either as bystanders in a group session or for content creation. That, for me, is the real turn-on.