The typical smart mirror film is Gila mirror window film (https://www.amazon.com/Gila-Privacy-Adhesive-Residential-Control/dp/B000H5XTKG). I got mine from Lowes in the U.S. It is a lot cheaper than two-way glass, and the quality isn’t mind-boggling but it’s not bad either. I think it’s 30% transparent but you can check that through the link. I applied my film to acrylic and it worked well enough–I’d recommend it if you’re on a budget.

It did work fine for the monitor I am using, right up to the point where I let the raspberry pi touch the metal portion of the back of the screen and shorted it (the reaspberry pi) out. What I did learn is the area has to be clean as an operating room when you are cleaning the screen before you add the film or you for sure will get a crappy result. MW