I had a Sears lawnmower. Bad idea. Electrical problems were tough (for me) to diagnose. Parts are mail order only, with no local dealers for service, and no telephone tech support from Sears.
My point being consider a brand with a local dealer if possible. I'm also told some of the Chinese brands have problems getting parts.
Top speed with mopeds can be a major problem. It used to take me 1/4 mile to get past a moped with a tractor trailer. The moped would travel at around 35 MPH, and for me to get from the 35 MPH that the moped held me back to, to 45 to pass took quite a long stretch of road. A recipe for a fatality in the event those little wheels should strike a bump or the like. I had a special word whenever I saw a moped ahead - it starts with F.
