I ordered a bike adapter termed "Freelock" from Stel Orthopedie in the Netherlands.
The device is a socket-mount only piece; there are no required handle bar mounts (as the Mert hand essentially is a two-piece adapter).
The Freelock metal adapter goes on the arm, obviously. But it ships with a hard plastic grip to put on the bike handle bar, that appears to be specially crafted, but due to that hard plastic grip's smooth and hard surface I figured better to use normal soft rubber handle bar covers - better angulation, softer shocks, better dampening, easier overall also with shifting use across several bikes. The Mert hand is great as it works so well, but it is a bitch to always reposition the handle bar side part of the quick release adapter.
The Freelock also has a quick release mechanism. The "thumb" pulls out and the spring (black plastic button to turn screw) can be set from anywhere between totally light weight to insanely tight.
The original adapter was ordered to measure 16,0 (000) mm, and that did not quite work out; there seemed to be some amount of bright gray coating that resulted in the adapter to be slightly larger.
So I jammed the thing into my vice (see vice marks of the Freelock's rather soft metal, below) and ground the adapter into fitting submission; then mounted in on the Puppchen wrist adapter.
So I rode my race bike around the block (mods: see Gerber 1981 bike mod page; essentially featuring a cable stop with removal of downtube shifters, and handle bar mounting of Silver shifters; also, I installed a Paul duplex brake lever and installed brand new Shimano brakes for optimal performance).
Here is a socket camera view of that ride. Have not tried mountain biking through some rougher terrain yet, but I was more interested in getting a prosthetic adapter that also worked with a drop bar, and first tests showed that this could indeed work. >Particularly seeing as if I do have a drop bar lying around for that bike.
Update 2018: riding a fixed bike handle bar adapter caused me serious back pains after some 15-20 minutes already sometimes, so I switched to a more dynamic way of riding bikes. I now prefer the Toughware Equilux or TRS Prehensor. Also, you want to switch sitting position on a road bike that has a drop bar.