Tinted / Iridium Visors & Aftermarket

Hello all,I was wondering if someone could help mke. I have a Shoei XR-1000 helmet and i am looking at getting a dark visor or Iridium visor.

firstly, what is the difference and secondly what do the ‘aftermarket’ ones compare like?

If i can pay £25 less then i will! i just don’t want bad quality.

anyone know of decent places to get one from? obviously i know race visors and visor shop but hopefully some people will have come across a gem or two!