Skiman,
they may slow down the plane better, but they don't make that big of a difference. On planes our size the 3 and 4 blade props are actually less efficient than a 2 bladed prop. And in the 6 years that I've been teaching students I haven't seen a student yet that hasn't messed up at least one prop when they start learning to land. 2 bladed props are cheaper to replace than 3 or 4 bladed props.

Ken