I believe it is a plant mister, I have friends who use them, some because they can scrunch the pumper with their elbows (whether from keeping their hands cleaner or because of arthritis type issues). Some can be quite fancy/heavy others lighter, it all depends on what you want and how you want to use them.
I'm a pinner, never have been much of a starcher, even when dealing with bias edges, but I was doing a little prototype block today that was making me reconsider that...