Comparing those are like comparing apples to oranges. One is fixed pitch, and one is collective pitch. Both are flybarless with their own built in gyros, and both can be bound to your DX6i. If you have collective experience, get the mcpx. I know you own a few of them. If you just want something that is just easy to fly and hands off stable, get the mSR. Well, it's the mSR-X now since it's flybarless with a 3 axis gyro, but still the same lol.
So the decision is up to you. Do you want a micro that is good for just about anyone that flys, or do you want one that's more like your trex?