OK, so I just got my screens, and they're what you would expect: fine meshed screens, portions of which have been blocked out to prevent icing from flowing through. Icing gets smeared through the open part of the screen to leave behind a pattern. I haven't tried them yet (I will next week), but I can see some immediate advantages and disadvantages relative to stenciling:
Advantages:
1. The screen is more flexible than acetate so it may conform to the cookie better, meaning less likelihood of icing underflow.
2. The use of a screen allows any pattern to be transferred, whereas with a stencil, all of the acetate pieces that remain must somehow interconnect or the stencil will fall apart.
3. A screen is perhaps less likely to get damaged because it's one big flat piece (with no edges that can get bent or lift up).
Disadvantages:
1. The icing consistency will probably need to be much more precise, because if too thick, it won't pass through the screen.
2. Screens are likely to require even more frequent cleaning, because any amount of dry icing in the screen will clog it. (The manufacturer - Gateaux, Inc. - suggests adding piping gel to the icing to delay drying times, so the screen can be used more than once before cleaning.)
3. Comparatively expensive.
Anyhow, once I test, I'll report back again. I imagine the screens will take a little getting used to.