If they're geting $4k  copy, I'd imagine there is something to these gizmos. I looked at them, and the frame itself is pretty simple- probably could put that together with some old bedrail.

The tricky parts are a) making sure those wheel are aligned - if the welder doesnt get that right, horrible things could happen. Then there's b) fitting it to the motorcycle itself. The Voyager brand "trike"  has a snap on, snap off belly bracket adapter that permit the gizmo to be removed when you want to find some twisties to straigten out.

Those rear wheels would have to line up with the rear axle of the bike in order for it to turn properly. Also, how do you manage the frame as unsprung wieght.  

Yeah, looking at it, it's just a few bits of steel welded together, but there was a lot of thinking and drawing before the welder came out.