If you don’t know why it’s a a bad idea with lots of issues, you haven’t been reading the thread. If you read the article, it’s not an inexpensive idea.
Funny that some of you compare this poor design supported by the hitch to axles attached to the frame like when the axles are fairly close together like on a dual/triple axle trailer.
Then, there is the generic problems with tag axles even if his design wasn’t so bad.
I get you trying to defend this poor design if you are his friend. Good on you for that. Unfortunately, this is a tough crowd. He would be better off the supporters just let this thread die. Then, those that didn’t know any better might consider buying one.