It's 1.42mb! Less than 2 mb? $10 isn't a lot of money for this much DLC, but it feels strange to give that kind of change for such a small download. It's like a software switch. Try not to think too hard about it.
If you're not hung up on technical details, this is a fair bit of content for 800 Microsoft points. You get three new characters, three new maps, two weapon skins and new Achievements. Oh, and fortification upgrades.