1) I enjoy it enough to carry it when I need to. I found a softshell case at a music shop that fits the UHK and my laptop surprisingly well. Not addressing preference, simply noting that it is more portable than other split boards I've used.
2) The UHK is built well and very sturdy. I've never questioned its durability as it's constructed better than most of my other keyboards (except for maybe my Leopold).
I use it enough that I've proposed getting a second one. Not because I'm worried about production or failure, but because it is a good keyboard and I use multiple computers. Though with the portability and a few cons (addressed in my other lengthy comment), I've held off from buying another for now.
The second fear for kinesis at least is largely unwarranted as the company has been around for nearly 30 years [1]. For something like the ultimate hacking keyboard, its future is less certain. Sticking to an open source keyboard where you can order your own PCBs is probably the most reliable in terms of longevity.
2) That was the reason why I've picked UHK - it is open source. Parts can be easily replaced. Though it does not seem it is going to break soon.
I wouldn't worry too much about that. These good quality keyboards will last for a long time. By the time it breaks, the state of the art would have advanced , you wouldn't want the same thing again.
Go for it.
1) I have no desire to own multiple of these for each of my working environments (home, work, and occasional remote from elsewhere). And no desire to always carry one around.
2) I fear making myself too attached to something which may go out of production. In case it breaks, I'd be sad.
To those who use these keyboards: are these legitimate concerns?