I finally got my KingKong 5040 tri-blade props tuned to the point where I feel I can comment on their performance. Long story short, I like them a lot. They are flexible enough to not be permanently damaged in a moderate crash. They are well balanced from the factory. They are cheap. And they produce an acceptable amount of thrust. If you are an all-out racer trying to get the absolute most from your setup, this is not the prop for you. If you are a freestyle or fun flyer trying to balance performance, tunability, and price, I think this is a fantastic choice.
As much as I like these props, they are not as durable as the two-blade version that I have flown forever. The hub on these props is a little thinner, and they are more likely to lose a blade entirely, or even for the hub to crack. My search for the holy grail of props continues.
You can buy these props here: http://www.banggood.com/10-Pairs-Kingkong-5040-5x4x3-3-Blade-Single-Color-CW-CCW-Propellers-for-FPV-Racer-p-1067875.html
KingKong has released a bunch of other multi-blade props in various shapes and pitches, so check them all out at this rcgroups thread here: http://www.rcgroups.com/forums/showthread.php?t=2580493