Advantages of this design:

* Stackable: it can be printed in multiple copies overnight from a standard printer, just remove the sprues with a wire cutter. Doubles productivity for small shops (and lets operators get some sleep!)

* Cheap/fast: Uses as little filament as possible, and can use both rigid or flexible acetate sheets, or Office Depot / Staples transparent sheet protectors (which are cheap, available anywhere, also come sealed). Prints quickly.

* Adaptable: Any transparent plastic sheet will do - both flexible and rigid sheets will fit. Only needs one rubber band or similar for holding it in place.

* Easy to clean: Microwaveable, and the sheets can be replaced quickly and without tools, so they can be treated as disposable. Can be washed.

* Easy to customize: The design can be enlarged or shrank as much as 15% without changes since there are no fixed-placement holes. This should cover most head sizes!

* Small: This can be printed on consumer grade 20x15cm printers (e.g. Monoprice clones)