Seems like a interesting idea but is it practical?
I could see some potential uses for this.
It seems to work in Star Trek, so why not now
I think a head strap is far more practical.
If you cant hold the light in your hand, then you likely have something else in hand.
You either want to shine your light on that thing in your hand, or in front of you.
This doesn’t seem good for either scenario.
Just rubberband a light to your arm and decide if this arrangement is for you. 
+1 for headstrap being more practical to free both hands
These are probably more useful when diving. You have your hands pointing forward all the time.
headlamp or head-band mount is more practical IMHO.
Sometimes I clip my Manker E11 onto my watch strap… but its only moderately useful. Much prefer a head-mounted light, shrug.
I gotta say “pass.” For tactical use, this is actually pretty good while you’re saving up for a good pistol-mounted light and holster (how many years have I been doing that?). And it works with a Convoy S2+.