due, sticky p plates for windscreens ARE illegal.
just mount one gauge all the way at the bottom of the a pillar where it meets the dash, thats where i have mine, cops see it all the time and dont pull me over, i suppose they could still get you for it being a distraction from the road or the lights too bright or something though.
we will never win just try to minimise the damage
i like cops, some are just worse than others