Never heard of it. I guess the extra light can help a little with visibility. But I would think that most people would understand the turn signal of the outstretched arm. Would an additional turn signal light be necessary? It’s also two more batteries that you would have to worry about recharging if you use the signals often.
$55-65 is also a lot for a pair of gloves.
I think I’ll probably pass on these. If others find them useful, I would have no problem. (Unless the light is so blinding that it affects people riding behind the glove-wearer.)