Its a matter of personal choice but IMHO radar detectors are of very limited use since there are very few radar guns in use these days.
I'm not sure what use a laser detector would be in reality because I'm pretty certain that until it can actually 'see' the beam it can't detect anything, and at that point the beam will be 'seeing' you.....
And of course, drive off the ferry into France with one and you will lose your vehicle if stopped.