There is an important question of law that is missing here;
Dark visors are not waranted shatter proof like your clear road visor (lacks the BS marking) and it is THAT which renders them illegal and not for road use.
It is illegal not to have a visor fitted to a helmet if it was designed to take one. The law is very silly like this as it is ok to have an open face helmet. Having spoken to traffic cops they perceive dark riders to indicate aggressive riders and it is an EASY EXCUSE to be stopping you, few prosecute though for that alone Excess speed +naughty plate+dark visor begins to fail their attitude test though. They prefer you to wear shades in your lid. These will cut and injure you in an off. My early ride to work when it is sunny is DANGEROUS with my clear visor, I am blinded by the low sun so much prefer my dark visor. I have been caught out in the dark with a race visor and it is bloody dangerous but I think most people/police use common sense, day time and the offering of a clear alternative being carried is fair dingcom. Most police don't know why the visor is not for road use (the shatterproofness lacking) though the darker visors would fail a "tintman" test, this is a device that they test light penetration on tinted car windows that boy racers black out there car windows with. It has been no biggy in my 20 years riding but I would expect to be done if I got stopped in the dark wearing one. Other than that its no drama really.