Yeah those propellers can be quite sharp. I use a glove so that the glove gets torn up. A chicken stick is good too. The rubber finger guard works well too.
I have done that a few times, when in my zeal to get a engine to run, I forget to put my glove back on and give it a quick flick, which usually doesn't turn out well.
Another thought is for test running a engine, use a sanding  block to dull the propeller edges so they aren't sharp. After getting a engine to work Ok, then you can try a better prop on it with more care for finger protection.