Ok, so courtesy of Saluki, I got to spend a little time with one of these... no gigs with it until next weekend, but some interesting results. I compared it to my stack of AE210's and it sounds a lot more evenly voiced to me. The AE210's seem to have more going on around 500Hz or so, and then again somewhere around maybe 200Hz. Definitely a lot stronger through the mids, but not as much low end extension as the AE212... pretty much the same up top, but I think you can hear the high end better with the AE212 because it's so much more even through the mids. I'd also say the AE212 has a really nice transparent deeper bottom to it than the 210's.
So to kinda' tie it all up, I think the AE210's would be a lot more effective at cutting a nasty mix with a bit more chest punch, especially in a boomier room (which is what I mainly use them for), but maybe not give you as big and sweet of a sound as the AE212, and with not as much edge in the upper mids and highs as the AE212.
One thing I do still like better about the AE210's is I can stack them on-end and get a much taller bass rig for better monitoring on smaller stages. This will not matter to a lot of folks, but it does me.
So from a purely tonal point, I really like the AE212 best. It has a much more 3D tone... seems like you can really pick out the details of the sound of your bass, but from a purely functional point, the AE210's may be more "effective" in some cases.
Keep in mind EQ can always be used to adjust... just FYI on "base tone" at least.
The gig next weekend is in kind of a rude place, but I will be able to get enough away from my rig that I can just deal with pure tone. We'll see. If