B&S is an APUG advertiser but I am not affiliated with them in way other than as a customer.
The puddle pusher works very simply. The solution to be coated is dispersed in front of the glass rod. The rod and the puddle is then pushed across the paper. The action can be reversed coating in the opposite direction. Any excess coating may be wicked up with a paper towel.
I like the looks of it, and its cheap enough. Does it drag across the paper or roll? My only concern since I work with some very thin vellum rag paper.
It's best to think of the puddle pusher gliding over the paper surface. The glass rod is a hollow tube and the ones sold by have a glass handle fused to it to make coating easier.
You can coat vellum with it just fine but you wil probably wish to tape the paper down.
I have a large piece of plate glass covering my counter in my darkroom. This provides a clean rigid surface to coat on and can be cleaned when necessary.
Coating paper with a glass (or acrylic) rod works well with papers that doesn't curl / become wavy excessively, when they get wet. Very thin papers could pose a problem... You have to try and see if that works for you. If you have a neon sign maker nearby, maybe you can persuade them bend a small scrap tube to bicycle handlebar shape, and use that as the puddle pusher - I have several tubes (4" - ... - 13") made this way...