They're not wrong.
However, they're not necessarily right either.
First, F rating means that it can withstand
at least 0.88J, from an 0.86g
steel BB. The jump to B rating (16.2J) huge, and yet the few B rated glasses and goggles out there are not substantially thicker or more robust than the F rated ones.
Consider: Bolle Tracker II
Clear and
Smoke are both B impact rated. The
yellow lens is ostensibly F rated.
Is it reasonable to assume that Bolle would use 16.2J lenses in two out of three versions, but that the yellow version just barely scrapes past 0.88J? It's only 5% as strong?
A reasonable interpretation would be that grade F means somewhere in the range 0.88J to 16.2J. Most of that range covers airsoft use, and remember that testing is done using 6mm steel rather than elastic, frangible plastic BBs. The worse case scenario in the UK would be a ~2.3J impact from a ~0.5g plastic BB. I'd be surprised if that actually penetrated any genuine F rated lens. However, there's only one way to know for sure.
Which is the second point. I stress "genuine", because anyone can claim that their eyepro meets any standard that they like. Who's checking? They're self certified. Unlike with
motorcycle helmets, there's nowhere that you can go to check. And even if you could, and even if a company's eyepro had been submitted for testing, and even if it had passed, that says nothing about what actually makes it through production. Remember, China is a nation
where businesses poison babies to increase profits.
If you want to be sure that eye protection can take a point blank 2.3J / 0.5g sniper shot, the only way to know is to test each individual item on site.
Anything less is Health and Safety theatre.