check below.

I have a cheaper method...

it's called mud.

Snow works in winter just as good.

If all else fails, a baseball bat to the camera is quite effective.

Quoted from 1

check below.

Sure for a flash camera.  But in most cases it will only partially obscure as the angle has to be correct to effect the entire plate.
Chances are that there is a software algorithm that could discern the plate numbers even with the glare.  You just have to hope that they don't have the man power or time to process incomplete obscured photos.

Mythbusters had one episode on that.
That product was busted.
Only thing that worked if you 400miles hour the only way for it not to see the car.

Are you really that terrible a driver that you need this crap?

What I've been seeing more and more in Ontario are rear license plates that look like they've been washed a thousand times (i.e. really faded).  It may be bein gdone intentionally,it may be a defect in the license plates, but I do know that our inlaws travel the 407 more now that their cameras have difficulty picking out the plate # (usually they only get charged one stop if at all).