I think the reliability of these units would be good enough. Tube audio gear is inherently simple stuff. If you buy a kit, and are handy enough to put it together, you can probably also fix a fair amount of what may go wrong down the line.
However, like kw6 states, you'll never get the Jadis transformers. Transformers are by far the most critical piece of a tube component, what one should put their money into, and among the biggest reasons a Jadis is a Jadis. I'll also note that the passive parts appear to be different (the Jadis capacitors, which like the transformers, you'll never get), and I have had enough bad experiences to now understand what a good friend told me, "Jadis voices their equipment, and most people look at some of the cheap parts used, and figure they can make things better via modding it. Not so easy." Indeed. I've paid a pretty penny setting my amp back to stock, and the improvement was more than worth it. The unit using a PCB instead of being hardwired is another thing. I never understood Shelby Cobra and Mustang clones, but they sure are popular with others.
If your only goal is to copy the circuit, it seems like a good deal. I could think of worse things to copy than a Jadis. Why not start there?
Then again, you may have issues with someone blatantly disregarding intellectual property, as it's out and out plagiarism - or, maybe you don't...
