They are absolutely 100% legal. The reason radar jammers are illegal is due to the fact that radar bands are governed by the FCC (thus messing with those frequencies would be a federal offense...serious consequences if found to be using one of those devices including huge fines and possible jail time). The laser band however, is governed by the FDA...so you can legally jam that frequency all day long with no consequences whatsoever.
I have a good friend of mine who just happens to be a FHP...and the laser gun gives error readings about 4-5 times out of 10...so just the fact that they get an error reading is nothing out of the ordinary. I have the escort version mounted in my car along with the SR7 and it works like a champ.
Installation is a little more involved than putting it in your windsheild and back window. If you installit like that...it simply will not work. It has 2 front sensors that have to be installed in your cars front grill area and a rear sensor that mounts to your liscense plate. It has to be in the area that a cop will target in order to be affective. Laser does not work well on areas that are not flat...hence they will point it typically at the center of the front bumper and liscense plate for the rear. I will attest to this item working as it has saved my *** numerous times.