The hand held laser units have a low magnification sight and are good for many 100's of metres. Generally further than most people are looking or paying attention to.
Some laser based parking sensors can interfere with cop systems. Luckily they detect interference and turn off...
There are rubber'like inserts for filling up the T-slots. Google "T-slot rubber insert"
Those who don't use the slots and like a bit of grip, don't want sh_t in the slot - use the insert.
For everyone else, go naked.