That trailer looks like the old made in Oz/NZ Uni-Go trailer. They seemed to be a great thing, leaning through corners etc. I think that company was sold or moved their stock to the USA a few years ago. Uni-Go have a US site
https://www.unigotrailers.com/
It's interesting that the MadMax trailers are made by Unison GME, likely the same people from the name, or perhaps just a co-incidence. They (madmax) have popped up in mags or on forums from time to time for at least the last 5 years (
http://www.m109riders.com/forums/showthread.php?t=127606 ), saying that production and sales are about to start....
I note that the website that you linked to has entries dated 2016 as the latest news:
Have you seen a completed trailer for sale, or just a another press release about some road trial or another promise to make one?
I'm no engineer, but I don't see why the pre-production period for this type of trailer should have taken so long, so there must be some substantial hurdles for David to overcome.