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those XYZ jobs (look a bit like a product launch event stand with wheels on)
Two weeks ago I saw somebody in my street with one of those; not the normal Bullit-type setup though, it was more like some sort of "car" (frame going all around him), the whole apparatus stuffed with vast amounts of cargo (read: crap).
Should have taken a quick picture really, that thing was quite something.
Ridden pretty much every cargo there is including those XYZ jobs (look a bit like a product launch event stand with wheels on). Found when riding a UA that I do a tiny zig zag constantly, not sure if steering head angle/seat tube angle/BB so far forward/steering ratio/combination of all those things. They do have good payload solutions.