my parallettes have a pretty big diamater for my hand. i feel that they have to stretch a bit to secure a grip. because they are a bar, i do feel that i am able to grab tighter and be more secure than on the ground, but for those split seconds where my hand relaxes too much on the paralletes, the uncomfortableness is much more pronounced than it would be on the ground.
i did l-sits on the parallettes today and that felt ok though. my hand probably gets aggravated when the wrist stretches only. that and the muscle ups