I have one AOC E1649FWU USB monitor and many problems.
Xinerama don't work.
I tried to use udl kernel framebuffer driver, but it don't work as well. Original udlfb driver works only as main monitor. With udlfb I can open a fbterm or display a image with fbi but this is prety much useless, because the monitor don't update if the user swith a tty. Same if I use a separeted xserver for it.
I'm trying too use xinerama emulation with xnest + xdmx. If works, I'll report here.
You can try this:
http://iain.cx/articles/xinerama/