Depends greatly on the state (and in some cases city too) you live in but many have speed limits on them of 25mph (among many other restrictions based on motor wattage breaking them into classes). Any faster, pedals or not, it's considered an electric motorcycle with all the restrictions that apply there.
But the biggest issue is the lack of cycling infrastructure in general. A shitton of the US has little support for that kind of transport, or any support for those not in cars.
And there's legal restrictions on what kinds of roads you can ride on as well.
It's a headache.