The first issue would be accidentally applying the throttle by pedalling, either by bumping them or instinctively trying to get your preferred foot forward. On a bicycle you can pedal forward without applying a driving force as long as you do it slower, with this thing it's going to detect the cranks moving and drive the motor. The second issue is trying to modulate the throttle when leaned over, scraping pegs on a motorcycle usually isn't too bad but a pedal strike can be enough to cause a crash. Lastly, just modulating the throttle in general is going to be finicky, at least with a bicycle you have some feedback to control how fast you're going but with this thing if you pedal just a bit too quickly you'll be breaking speed limits, flying off the road when you get to a corner, or slamming into the back of cars.
I have a fair amount of cycling experience and I've ridden fairly powerful electrically assisted bikes and there's no way I'd feel safe on that thing, I can't imagine the carnage that a less experienced person would cause.