We get along way to good here for me to start anything so I'll hit the stop button on this if anyone wants but the lack of restraint seems to be the problem here not the hand start.
We have had both happen to our club members. One was with a smaller 20cc gas engine where the plane slid back in the hold down and when it started lunged forward and the pilot, out of instinct, grabbed for the plane, next stop, ER for stitches. He has healed up but never hand starts any more. The other was on a 3W 157 CSTS with a glove and it kicked back, HARD. Next stop, ER for a few stitches. the glove definitely saved fingers on that one but, the RCS could have saved a trip to the ER.
I hand propped for a long time and decided to give the RCS a try. It took me a bit to get used to it and not practicing first cost me an expensive prop. Not the fault of the RCS because I continued to use it after on the same type of prop and so far it has worked flawlessly.
The only prop I see an issue with would be a P-Tip prop. The props with the tip that curls back and up from the trailing edge of the prop. You wouldn't be able to get a smooth roll off the end because of the tip.
Not trying to start an argument, just telling what happened to a couple of our members. I will say that the RCS has saved me a possible trip to the ER when my 180 kicked back because I decided to not flip the prop hard and it kicked back. When it did it about took the RCS out of my hands and woke me up.