You buy the kit for around a thousand dollary doos and you just basically bolt it do your hub and in the fork and voilá, you made your bike into a long john. It even comes with some nifty thing to change the brakes from normal to cargo bike. Holds up to loads of about 150lbs in the box there.
I think it's a pretty cool concept from an enviromentalist standpoint because you can retrofit any of the million currently existing bikes without having to produce entirely new ones.
If you only occasionally could use a cargo bike switching from one thing to the other takes about 5 minutes apparently so storage is easier even if you don't leave it permanently attached.
They just need to figure out a way to include an e-drive here, as it is it's basically for young, fit people in flat areas as it stands, allthough seeing as it already integrates into the hub it feels like a problem that could be solved.
Can't find anything on their website about it at a glance, it's probably a 20" wheel.
Which is where this gets into a very clear "yesn't" territory. 20" inch wheels arent't terribly uncommon, both for childrens bikes and folding bikes. They're usually weight rated to a far lower degree though as children aren't that big and most folding bike frames can only take about a 100kg, so they're often made to specs far lower, much more in line with 50kg per wheel (assuming 50:50 weight distribution for simplicity)
Now let's say your average bike weighs about 12kg / 25lbs without the front wheel, the thingy here has an advertised loading capacity of about 70kg or 150lbs. That puts you at 82kg / 175lbs with no rider on it with a full load. So it'd be suitable for people of about 18kg / 40lbs, going by usual ratings.
There is, of course, 20" wheels rated for higher weights, allthough I'd guess they're only from other cargobikes, some of the brompton lines, BMX's or one of the newer chinese import folding e-bikes or scooters, i.e. comparatively rare.
Could they just sell you a framekit and should they? Yeah, absolutely. Is ist understandable they don't? Pretty much