I don't know if 5 miles is long enough for the people who actually need it, but if I was a postal worker, these would be pretty sweet. And 1400 USD is cheaper than some car insurance here in Canada for young males.
At least in my neighborhood I think these would be more trouble than they're worth. It's a historic neighborhood so all the houses are built up on berms from when they dug the basements cuz the streets were full of muddy manure, so every walk up to a mailbox has stairs. Unless you're agile enough to go down stairs without doing the lock/unlock dance, these would probably slow you down overall.
I watched the video, which is why I called it the lock unlock dance. Note that in that video, which is obviously going to be the best looking version of it they can show, it's still a pretty significant pause in your motion, because the control is both motion and timing based. Doing that two times per house for the 10 miles or so a carrier walks is gonna get old.
It has a 3.0 Ah battery (not Wh, assume one 18650 lipo cell -> 11 Wh), comparable with a smartphone or flashlight. At a full 300W discharge, you're emptying the batteries in just over 2 minutes. You'd better have well-insulated soles before stepping on a pair of 150W space heaters, also, no 18650s are rated for 100C discharge, 20C is a lot and 5C is more common for the high-capacity low-discharge 3.0 Ah cells.
You get 5 mile range by using them like roller skates, using your own legs to power them. The motors are just to aid in walking up stairs and such.
I'm really skeptical these wouldn't just gum up after a few days.