Never seen or heard of such an item before. If it works, I'm sure there'll be a few folks here who would be interested in it. Check out the seller's feedback. A lot of problems recently.
I looked through the sellers feedback (all the negative and neutral responses) and didn't see anything specifically about this product. Most comments were about late delivery of filters etc.
Was I looking in the wrong place? Can you post some of the feedback you've seen on this product please?
I'd really like for this to work as it would be a real bonus for some of my shots.
I shot the UCI World Trials Championships in New Zealand (trials bicycles) last year and could have used it then to get better shots close in without disturbing the competitors.
I have the World Single Speed Championships coming up in a couple of months in Rotorua Forest, New Zealand and can see it would equally be a bonus there.