We would all love for our show heifers to turn into great cows, but the reality is that it's somewhat pointless to worry about that. If you are showing, your priority almost has to be to select one that do well.
There's too much variability in any breed or crossbreed to think you find the great looking show heifer that will also make the great cow. For the most part, my best looking heifers hardly ever make my best cows (as far as raising show calves). I find that problem more prevalent with my purebred Angus than even with my crossbred girls.
That being said, MAB females should have a chance to make fine mommas. I've got some being bred this fall for the first time, but none that have calved yet.