I have a DevTerm R-01 and it is basically a beautiful $200 novelty cyberdeck that sits on my desk. The R01 version in particular is greatly under powered and is really only usable with twm and a Xterm.
I mostly use it to read gopher:// and the kids love printing things off using it's thermal printer.
It's not great but not absolutely horrible. Two-finger typing most of the time and the overall feel is stiff, but not too stiff.
I usually hold it with my hands and use my thumbs, like a Game Gear. Re-mapping the "d-pad" joystick and "yxba" buttons to arrow keys and hjkl [1] makes it easy to read and navigate text content on it (hence of gopher://), especially with the wide and high resolution screen.
It's size is what turned me off most about the devterm. I would be much more tempted by a device just a bit bigger. This[1] blog post has good pictures, one next to a DVD case for size comparison.
I mostly use it to read gopher:// and the kids love printing things off using it's thermal printer.