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High bar does a lot for stiffness /resistance to bending on its length. Step through frames need huge girders to get anywhere near close to that of a high bar. On a regular bike there is a difference but its not bad, on a cargo its an issue.
UA if you have a decent load on you can feel the front end of the frame vs rear triangle twist under hard pedalling /cornering forces. On most of the trike cargo bikes (babboe /cristiana) that twisting goes from "sort of noticeable, but not an issue to an average user", to "holy fuck when you turn left, these thing bends so much the back end turns the other way" and you get a speed wobble at 8mph on a gentle left hander.Last year a group near me tried a few 2 wheel cargos, decided they wanted a trike for some reason (i think folk expect them to be more stable?) bought one online without trying one first (I had warned them but...). Thought it was great for kids. Then on 1st week of using it got a speed wobble on (10 to 15mph)lost control, and turned over into the road. Kiddos were fine as all had seat belts on,the dad got a sprained wrist, could have been worse. One wheel, bar and a brake lever mangled, but it'll survive.
I ride a UA for work (not the family though) and used to ride a Bullitt. Both ride totally fine once you're up and running, the UA position is more upright, at least with the stock stem/bar combo. The only thing to consider is the slightly larger size of the UA, it makes it a bit more difficult to manoeuvre at low speed and gives you a bigger turning circle. One upside to the UA is the step through frame, I find it a lot easier to get a heavy cargo bike on to it's stand when I'm not on it and it feels a lot easier to control the weight of the bike as you're getting off with the Urban Arrow. Honestly though, it won't take you long to get confident or comfortable riding either of them, they're not that drastically different.