What are the differences between the two?

Has anyone ever done a comparison between API's two preamp modules, the 212 and 512? And we might as well throw in Brent's version of the 312. I like the idea of a simple, straightforward preamp like the 212, without extras like multiple I/O, etc., and its also a couple of hundred cheaper than the 512. The big downside is that it doesn't fit in my 500 series rack empty slots.