What is the difference between the mirage, and the mirage plus? Which is better for me?

Just received my first trial prop from Brett @bblades. I am trying a Rev 4 19p. Hopefully the weather will clear up for the weekend and I will get to try it. It does look pretty cool though. Just curious as to what the function is of the holes are in the back of the prop? I can't wait to try it!

I ran the boat yesterday and Brett was right on with the rev 4. I got 51 mph gps out of it at 4650-4700 RPM. The drivability of the prop was great. It was real smooth, planed with ease, and made the boat feel light and nimble. All of this was also with the boat breaking up! I must have a bad wire because I heard spark jumping at idle. They are only on their second season, but it is a boat! I have to put wires, cap, and plugs in it and then retest. So far I am pleased...I just hope the RPMs don't creap up when I get rid of the miss.