yes they works and yes they are highly illegal !

it only works if its put in the right place , just above your number plate in the middle or just below it again in the middle as this is where the cops will aim the gun

its helpful that it will only activate for 5 seconds giving you time to hit the brakes and then they can get another reading but if they suspect that you have the device fitted expect big problems when they find it

it has been know for people to use the "its for auto garage door or auto gates officer" as they work the same way