Well around where I live, Maryland, you are able to ride them on the sides of the roads, but only local, NO HIGHWAYS or ROUTEs as far as i know.
My friend has 4 mini crotch rockets, yes FOUR. He only had TWO there when i to his house last week and one of them had a top speed of 40mph, and the other was a little bigger and maxed out at 60mph and had thicker tires, big enough to pull little tricks on.
But they ride them around here all the time, they are very un comfortable. My brother told me they move pretty quick for 50cc, but thats just what ive heard from everyone.
And they are 2 strokes, so theres not a whole lot you can do to make them much quieter, your neighbors might think they are hearing a Chain Saw untill they hear the sound moving around,lol.
If you have the extra money sitting around, why not....
But if you have to save up for a while, your just better off saving up for a dirt bike, or a motorcycle, or go cart.