Here's something to think about, a 12 inch prop turning 12000 rpm has a tip speed of 628 ft per second. That's about half the velocity of a .22 long rifle bullet. It's about the same velocity generated by a 200 grain .38 special bullet shot out of a snub nose revolver. Do you really think that a rounded leading edge would make any difference should you be unlucky enough to get your finger in the prop's way? Bullets have round leading edges after all.