Polchoir is French for "stencil." I just learned this while researching public domain Art Deco and Art Nouveau stencil designs!
Why public domain?
The good about buying stencils (or stamps):
When you purchase a stencil, you are supporting the artists and manufacturers that designed that stencil. Everyone wins.
The bad about using bought stencils (or stamps):
You are placing limitations on how many times you may use that stencil in designs for sale. I read the fine print on most things... I don't recall if it was a rubber stamp or a stencil but the item said "up to 10." If you're into scrapbooking and giving away your handmade cards, etc., you have no limits on how you use your purchased stencil (or stamp).
As much as possible, I seek to make my own. It's therapeutic making the cuts as well as freeing, lol. Cutting vinyl is sometimes better than drawing or sketching.
The photo shows one of my latest stencils, hand cut 10ml vinyl using an exacto knife and scissors. I used a slightly crumpled paper sheet to test it, with some "leftover" paint and a make up sponge. When I find a design I like, I manipulate it on my iPad, print, and then cut.