Open carry is legal in Alabama so there is no legal problem whatsoever with exposing the mags. Or the gun. From my understanding open carry is legal but not too common so there is a bit of misunderstandings with some police. I researched this pretty heavily as I just moved out to DeKalb County to (eventually) marry a gal.
The real point to ponder is what happens in states where open carry is banned, such as Florida or Texas or a few others? I would strongly recommend concealing the mags. Police in such states tend to take an extremely dim view of what they percieve to be illegal open carry, as they consider it a "mark of a police officer" and get highly irate when their view of their "private privileges" are displayed in any fashion by "the peasants".
Mind you, from what I've read on the Alabama open carry forums, some AL cops feel the same way, but they lack any legal leg to stand on.