Oddly, I had a chance to test mine out this past weekend. I own the Helite GP Air Track Vest, so I can't speak on behalf of their other vests.
My incident was a lowside, probably about 50-60MPH in a carousel turn (someone spilled coolant
) The only thing I noticed was that I started on my back and then I think the bike tugged me and flipped me on my front at which point the tether presumably activated the airbag. I did not feel anything when it happened, except that when I got back up I couldn't move my head at all (great stabilization). All that said, I ended up with a broken peg and a lot of dirt, but had no problem reloading and going back out.
This is one thing I do prefer about the Helite vs the Hit-Air, is there is no need to carefully repack the airbag. It's all self contained without worry of folding incorrectly. (I did watch someone else do this once with the Hit-Air Race). The second is it's leather in all the sliding zones. The Hit-Air is, as I understand, largely textile - which while abrasion resistant, may not do as well after multiple incidents.
I also have no issue with the tether in it's location. What took me the longest to get used to was A. remembering to put it on before 1st call. B. remembering to hook the tether up before I got on the bike.
The only con's I have for any vest is it's kind of difficult for me to put them on with my helmet on already, so that took some change. And it's a little difficult to attach the tether with gloves on for me. The only con I have for the Helite is that it is leather, and it covers a lot of area on your body. My suit is perforated, but it is notably warmer at rest with the vest than without. When you're riding on the track, I don't know that I've ever noticed.