I'm so fickle.
I went ahead and flashed back to the jetBook firmware after fiddling with the M218B interface. It was actually quite straightforward: after the first flash, it gave me a M218A+ startup screen. Interesting, especially since I hadn't seen that screen even with the M218A+ firmware loaded. I just did a hard reset and a second flash. As before, when I thought I bricked my jetBook the first time, the jetBook seemed like it was stuck, but the firmware update screen came up after it sat for a few minutes. I held power and right for about a minute before setting it on the table and waiting it out.
For good measure I reset to defaults after jetBook successfully loaded. Oh, and got it back to English instead of Spanish.
If anyone else wants to try it, I'd summarize the advantages as:
-Variable PDF Zoom
-Ability to choose any font for TXT
-Basic TTS with a bunch of odd effects
At a loss of...
I don't see much of a reason to use B instead of A+. I tried playing with JAP, which seems to be good software, but the Wolf output file it gave me from PDF was 25MB (PDF was 1-2MB) and wouldn't load. Oddly enough, HTML wouldn't work for me. Never tried flash (SWF). In the end, I decided I liked the convenience of ePUB for novels and didn't want to make custom files that would be obsolete with another reader later. TXT of course is OK, but the PG texts aren't always pretty.