a very good idea. Still not UK road legal though.
Stupidities of UK visor law:
Sunny day, dark visor = illegal ("unsafe")
Sunny day, clear visor, squinting to try to make out the road = legal ("safe")
Sunny day, clear visor down, sunglasses digging into temples causing headaches = safe
Sunny day, clear visor up for venting, sunglasses digging into temples causing headaches = unsafe
Middle of the night and dark visor = unsafe (duh)
Middle of the night and clear visor down with sunglasses on = safe (ffs)
Middle of the night and clear visor up with sunglasses on = unsafe
Photochromic visor at any time = unsafe
Riding around in the middle of the night wearing nothing but a thong, lid and sunglasses with a clear visor down = "Safe"; lift the visdor up and now you're breaking the law.