I have one and it did work but I took it off as it can get risky using it. Basically if you look head on at the plate, you can still make out the plate number but if you look at plate at any given angle, it will blur out the plate number. It seems like just a clear hologram film or some sort. I tested it out on the speed pass toll booths here in NJ because my EZ-Pass toll tag didn'thave any funds on it and here in NJ, if you run through the speed pass lanes with a dead speed pass tag, they photograph your license plate and send you a fine in the mail with a photo of your plate running the toll. So I tried it out for almost a month and not one ticket in the mail for running the tolls. BTW, they really do send you a photo of you running the tolls here because before I even put the photo tag blocker over my license plate, I had received two ticket fines for running the tolls.
My truck does not have a front license plate as I chose not to mount one even though I am supposed to have one in NJ.
Funny thing is I promote alot of Import Car tuner events and they sell these sprays and plate blockes at the shows. Thats how I got mine.