They are routinely modified to exceed legal speed limits and owned by 10 year old or younger kids. Going nearly 30mph on a footpath whilst holding a mobile phone.
I think they are also unregistered.
Easily modified to go as fast as 50 MPH on a chassis not designed for it. Drivers aren’t licenced and often are young kids. No registration. No insurance. No training. Very hazardous to pedestrians.
Pedal fatbikes for riding on snow and sand have existed for at least 20 years I’d say.