I actually own both and have been using both of them for about a year now. They play completely different and it's easy to get used to one and play well with it and try the other and have your game be thrown off by the transition. Sometimes I'll play with one for an extended period of time and will think of selling the other, only to realize there's some qualities of the other that I really do like.
To put it simply, I've realized that when I play games/sets, I do much better with the MP. But I actually prefer and love just free rallying with the Pro. I love the pro for its thick feel on impact. It feels soft and gives you small ripples of flex, but uniformly is pretty rigid. I can definitely hit a flatter ball with the Pro and the ball moves according to how much extra you hit into it. The racquet almost asks you to throw your body into it a little more and I love it on my one handed backhand. But I yield much better results when playing actual sets with the MP.
The MP has a more stiffer feel. Not super stiff, but stiff and slightly flexible. A little bit like a babolat pure strike with more weight. The MP also has a much higher launch and trajectory angle. I can hit a medium stroke and get. a medium to fast ball. As opposed to the Pro where I needed to thrust a bit more of my body to get a more heavy ball. That's more easily done in a stationary rally setting, but when your opponent is moving you, it becomes more difficult to throw your body weight when you're moving around the court. The MP is much easier to return. In fact, I believe the return is the best component of the MP and since that is how you start off the point when you're not serving, it ranks up there in importance.
I was playing a very good player who had some good movement on his serve. I played the first set with the Pro and could not really find a beat on his serve. Even when I was making contact with the ball, the ball would go more errant. We didn't play that many rally points on his serve because he was holding so comfortably. That put pressure on my serve and I lost the first set 1-6. It was closer than the score with a lot of deuce points on my service, but you only get to serve about 3 times in a quick set like that. The second set, I actually tried the MP and did much better. I actually was located his serve much better and the contact to follow through with the MP actually allowed me to put him in some very defensive positions to start off his serve. The more pressure I was putting on his serve, the more my game grew and his serve ultimately weakened. I was also able to get a lot more spin and power without thinking about having to generate all the power. I jumped out to a 4-1 lead and ultimately won 6-4. But I felt much more comfortable. And I actually felt like I had the blueprint to beat him a third set.
I'm transitioning away from singles play and mainly play doubles to preserve my body as time goes on. I think both are really great racquets and I kind of stick to the rule that when I hit against my 4.5 / 5.0 friends, I usually play with the pro. But if I play singles set, it's easily the MP. For doubles, I can use either, I do notice that I play a bit more methodical with the pro when I have time to plan out my shots. But I can play more fast and loose with the MP. In this regard, it doesn't matter which I use. But I am glad I have both to where I can switch off.