Screenshots my ass, you do it :P
Yes, you see more terrain... take the usualy round minimap and draw a square around it, that's what you now see. The arrows (town/corpse/party) still stick to the circular mask tho, there's no way to change that. Also tracking abilities will stay in the circular mask, I'm sure blizzard would consider it unfair if square minimap users saw more on tracking than roundies.
Tracking abilities probably stick to the circular mask when you're zoomed in. Howver, they only cover things that the game server has registered with the client. This has a 100 yard range (although lag has a major effect here), while the minimap has (IIRC) a 125 yard range.
Theoretically, you could have a tracking skill "all world objects" that would show anything that's not part of the area map itself. And that would be shiny.
How does this handle the various mods that make buttons on the edge of the minimap? I'm just curious, as I have no intention of getting this particular mod. I'm a round peg-round hole kind of guy.