I own several bike trailers, built a few cargo trailers myself, and ride with them a few times a week, so I'm going to chime in with some thoughts after looking at their Vimeo page, which inexplicably has more information than their website.
The Convoy appears to be a standard bike rack built atop an electric unicycle. I say this to illustrate that it's offering maybe 30% more carrying space than you could reasonably get with a rack over the rear wheel of the bike.
Cargo layout image:
This is the best shot I could find in their videos.
The most striking thing to me is the use of a 14" wheel, yet the cargo area is the same height as a rack on the bike. If it was a bit longer, the centre of gravity could be lowered quite a bit. Though the compact nature could be useful to people with tight space limitations, I can't help thinking a long tail bike would be more versatile.
12kg weight for 50kg of cargo capacity isn't too bad, though my most used cargo trailer weighs 22.5kg with about ten fold the carrying capacity. It's much longer though, bit over five feet. Storing something this long isn't problematic for me though - my next one may be longer.
For a trailer that attaches to the axel, I like the connection design they've used (similar to the Burley Coho XC) and the tensioner being simple and effective for applying pressure on the powered wheel. It is also a stylish addition to a bike, which can be important.
The self steering aspect is quite interesting to me, though I'm not really sure it is needed for something with one wheel. The wheel does need to steer, given the trailer does not have any articulation from the bike, but why it has active steering is something I don't understand. It'd be interesting to know if they tried a passive steer solution that didn't work since the wheel is so close to the bike or something like that.
Unfortunately I have little confidence there is a niche for a product like this as I believe the dentists are buying Urban Arrows.