There are alot of demos posted on the internet. In most of them a 'hotdog' is used instead of a real finger but, there is one (I saw it on TV) of the inventor that did use his own finger!
It IS impressive to watch but, as was said before, it WONT prevent 'kick-back'. I have had a few kick-backs on my Jet table saw (it does not have the saw stop feature) and in one case, my right thumb did hit the blade. I got the end of my thumb 'chewed-up' a bit but did not loose anything more than a bit of 'meat'.
It may have helped in this case but, the board that kicked-back still hit me in the belly hard enough that I still have a scar after 18 months.
Nothing prevents accidents but, knowing how to use a table saw and smart planning before the use of it sure helps.
Rog