I would urge that you buy a genuine Arai visor. Two reasons, firstly they are very good quality in terms of scratch resisteance and very strong, I had a race crash years ago in an Arai and landed on my face or rather doffed the tarmac with the front of my helmet enough to smash out the chin vent. The visor looked like it had seen an angle grinder but it didn't split or shatter, plus those 'easy to break' sidepods held up too, they are designed to slide rather than catch in the road I think so I can see some sense in their design.
Secondly, during a lean month last year I bought a Bob Heath replacement for my Astro and it seemed thicker than the Arai visor, unfortunately they were too thick, everytime I lifted the visor it merrily pushed out both side pods near the top tab a bit too much until they split at the edge -£25 to replace the pods.
Andy, try the amber Arai visor, they offer better contrast in wet conditions and at night, plus they have the bonus of making everyday look sunny and bright.