MLB at Bat is AWESOME. And it has been awesome since day one. I give MLB credit for really taking the mobile market serious, right out of the gate.
The gameday audio subscription for a pc used to be the same price as the app. And how can you not love being able to get the home feed for your team no matter where you are!? (and that's not to mention that baseball and radio go hand in hand).
If you're going to get it, get it now, and take full advantage of the free month. Really see this apps potential with mlb.tv video. They've updated the interface too, so while you're watching the game you can get a drop down menu to see scores, and the box scores. And you can switch to any other game from there. It's really nice.