Is an excellent question, DirtWarrior.
First time I rode one, was the first thing I asked when we got back. But man are they fun to ride. All the noise, fumes and vibes are behind you. They easily convert back to a regular bicycle with no chain or belt drag. Keeps regular pedals. So pretty awesome to get you to a park or bike trail. All around, a great MB.
I forget who but there is a supplier who sells (or sold) polyurethane rollers but I never heard much about em or tried one. Some one will know.
Are you thinking of building one?
Some detractors say the center of gravity with the drive above the wheel is a negative. But really don't seem to matter just puttering around on roads and I figure my 175 lbs is already on top. Also think the mount would be a great place to mount a rack.