They are generally one-size fits all, but at least from some of the discussion you can get an idea how different models look in the pictures and see what strikes you fancy.
I've had a few different cargo e-bikes since 2017, Fiido T1 currently fits my purpose and cost under $1700 shipped to my driveway.
I don't know how well a Fiido T1 would fit a person over 6' tall; but I'm about 5' 10", I've plenty of room to raise the saddle if need to.
I'm about 180 lb. with all my riding gear on, The Fiido has plenty of motor to get me going from a stop to 25 mph or above. PAS (Pedal Assist System) has 5 different levels, I rarely get above PAS 2 for my riding in NYC.
Cast wheels (instead of spoked) require zero maintenance, likely to be more durable, too; strong enough for my motorcycles, should be strong enough for my cycling activities.
I like the size of the Fiido T1, since it does not have the extra long wheelbase as my previous cargo ebike:
Currently Fiido is doing a recall due to frame failures, I knew they were bound to fail before my purchase; but I still get out on mine.
I've been instructed by Fiido to stop riding my T1, replacement bikes are being sent to those who are affected by the recall. I'm expecting my replacement T1 to arrive by DEC 2022 or JAN 2023. Meanwhile, I've little to no concern of riding mine.
Below are list of improvements for replacement T1 model: