A few months ago I spent a couple of hours at the Essex Police traffic centre in Billericay, Essex. One of the sections we looked at was the camera enforcement team.
NONE of the so called sprays work. They showed us an example of a picture of a sprayed plate. Yes, it was overexposed and the number couldn't be read. However, they then reversed the image (made a negative copy) and hey presto! there was the number, plain as day
The only thing that works is mud, but that is a pull anyway.
Besides, even if they did work, they wouldn't really help us guys driving modified vehicles. You have made your vehicle different, so you are easy to track down. Even so called standard cars are rarely identical - stickers, badges, scratches, aerials, roof racks, etc. If they want you, they will get you!
Don't trust your licence to the hype.