I bought one of last ever made 6 years ago. I spent about 4k$ on my two (do to US/CND exchange). The used price now (as insane demand, low supply), is insane.
I think last one i saw in good condition (a Pro-II usb) [early were ps2 connectors], was 4kUS, so +5k$ CND now. On the plus side, my 4k$ "investment" in my keyboards,
has netted me 6k$ profit :) but I can never see selling them, if anything having to buy if one ever break.
Its on a open source free hw site, will have to dig but if you google open datahand or similar probably be top return. Below is a good forum page
The Datahand isn't only amazing for minimal stress on hand, wrists, and fingers, but it also uses only magnets and IR emitters/sensors, (no springs or mechanical switches)
so I hear stories of 20+ years with ease, and probably no reason for not 50-100 year life spans. I have had 6-7 years, and one is like new still with daily use.
(the other has a bit of a glitch, that i have to attend to, but stays as my backup). They do require a good air blowing and cyber-clean putty cleaning about once a year.
The big benefit of the DH and the reason I got it is that there is nothing worst for productivity then type, reach for mouse, type (repeat 100K's times).
The DH has the mouse built in to the "pods" of the pointer fingers of both hands, so you can type, and mouse with no "going for a mouse".
By a simple lift of the right thumb on a lever, the pointer fingers move the mouse, the right pointer has one velocity and acceleration in n/s/e/w,
and the left another, when used together, you can do linear, and parabola pointer arcs with ease (when you get good at it). You can't do circles at all.
but its truly amazing. The mouse parameters are tuned in the unit itself, and each finger can have tuneed velocity and acceleration. So it allows across
a 40" 4K monitor in 1.5 seconds (my setting) with one tweaked more for fast velocity, yet just the left gives me about 2 pixel accuracy. (and you use together in any combo)
It is so nice to not have to use any mouse, touchpad, trackball, etc. The mouse is always just there, "at your finger tips", no additional movement needed.
I was actually looking a eye or head mouse at the time, but they were also very expensive, and jumpy, so the DH was my choice for optimal anti-mouse(pointer).
But I think I will eventually get a head mouse to compliment the DH mouse, so I can do big jumps instantaneously, then use DH to fine tune in as target approaches.
This works as screen real-estate gets bigger. But head/eye mice are still pretty expensive still. I do a lot of gui dev. so even thou i hot-key a lot (DH pro-II i have has
full programming of multi-key sequences, and remap), I still have to mouse like crazy, and with DH, its just magical. The adjust ability is insane, each sides 4 "pods",
each pod having 5 hits n/s/e/w/down can be lowered/raised, and moved N/S meaning you tweek it right, and you are moving fingers 3mm-4mm for any give key hit. And the palm rests
area also adjustable. And the two "hand boxes" are adjustable as well in L/R rotation for exact arm/wrist angle approach. And the whole unit itself has a foam on bottom (egg shell),
and it just sits nicely on your lap. [works well for me as I work in lazy boy 3/4 reclined to remove any possible back issues and poor posture.]
Only regret i had, given you have to learn how to type for scratch with them, as they don't follow qwerty (sort of resemble it 70%), is i should have gotten a better layout, as after 90wpm
you run into the problem you want to hit a few keys, and you can as you have fingers at the await, but the 2-3 hits are all
from the same finger :( I can remap mine (i think) , but to have to learn again, and to get from say 90 to 110 WPM, doesn't seem worth it. But it was still nice to
go from a 40-50wpm on conventional (with having to "look" for rare keys, etc, and taking my gaze off the monitor),
to 90wpm and never looking for keys (i do however have to crap shoot for ^ and ~ and other rarities now and again :) The keys are not marked, there is no point or way to, there is a visual guide above, but you don't want to use it, so learning DH promotes and make mandatory
pure memorization. But most of my typing now is muscle memory words, I rarely know what letters I type, just "type" words, which as far as I know, you don't type at 90wpm
by letters (too slow), you are just collective finger motioning/timing on a per word muscle memory (or joining the common sub-word combos)
I also suffered from MRI/CT type pains, and all went away with DH. I think IBM did a test and declared the DH the best keyboard every made.
-tl