As I mentioned earlier when the Hobart/Miller helmet first came out (the one called "the hood") it had the EXACT SAME lens as the HF helmet sold at that time (not sure what either uses now). When I picked up a HF helmet at the store I thought the shade adjustment switch looked familiar so I checked out the lens and it turned out to be the SAME EXACT "Chameleon" brand lens that was in the $200 Hobart I had bought a few weeks earlier and this was in a $49.95 HF outfit!
The Hobart helmet had a better shell and headgear but not that much better and the electrics were the same thing. As far as the time it takes to change to dark being a concern you can believe what you want but the mechanics of how the thing works means that the UV will be stopped regardless of whether or not the thing goes dark so it is not an issue. Where did I get this? Not from reading a label but from discussions with Jackson welding products early on when these things first came on the scene, the field reps came out and explained how they worked and did demos with a meter that measured the UV during exposure to an arc. The auto dark, even the very early designs, stopped the UV even in the lightened stage and it was explained to us then that the UV protection is not dependent on the lens changing shade. I have used the the Auto dark outfits since they first came out and this was in some very demanding conditions where shade change failures were common because of awkward welding positions causing sensor blockage. I, and others I worked with, were "flashed" many times often with large rod/wire and high AMPs while using both brand names and no-name gear but to my knowledge none of us suffered any problems from this. The Jackson rep said the hardest sell he had was to convince people that the shade going dark had nothing to do with UV protection and that they were not being exposed to UV during the time it takes for these things to change. The myth still persists even after they have been around for over twenty years and you can still hear those BS stories about workers going blind because the helmet changed shades too slow.
The fact is, Government standards or not, if any of that non-sense was true and you could harm yourself with one of these things the lawyers would be having a field day with the companies who sell them, to quote the Jackson rep "If you think convincing OSHA was hard you should have seen us trying to convince the company lawyers!". There are far more of the cheap HF variety helmets out there in use than the big brand names but other than a few "urban legends" not much is heard about them. Fellows stopping the UV is not rocket science (in the beginning it was done by smoking a piece of clear glass over a fire!
) and you are not depending on the electrics of these things for that protection so shade reaction time is not going to cause you to go blind from UV exposure.
One thing to mention is to NEVER use these, or even a conventional helmet, without the cover plates because even though the cover plate is clear it still has quite a bit of the UV protection!