I have a bunch of em and have tried them all over the place. One time watching a movie I moved one from the turntable motor to where the HDMI came out of the laptop. Immediately my wife says, "What did you do!?!?!"
Improved contrast and color saturation, the projected image took on a more natural dimensional appearance. Not cartoony etched like a video store demo under fluorescent lights look, but more like film. I mean real film, not the digital stuff they put on film these days.
So yeah, they work.