This is looking great! and congratulations BTW!
I've found riding laden cargo bikes in Sheffield a chore, even with (modern) mountain bike gearing. As soon as you hit a hill all momentum is lost and you're straight into the smallest gear, and it's still difficult.
Electronic cargo bikes are the only way in hilly areas. I've seen loads of riders on the road, in the Peaks, who I suspect used to have the fitness to ride there, but now don't, able to enjoy themselves on a e-bike too. They've definetly got their place.
I agree that in flat areas, there are better options, for inexperienced bicycle riders.