From the ad: "Once built the chain rubs the inside of the drive side dropout when on the smallest cog on a 8 speed cassette. This is a factory design flaw that can be fixed by adjusting your limiting screw so the chain can't go into the smallest cog or you could change it to a single speed or you could do something else we have not thought of."

I will have to rethink my recommendations about buying Gravity-brand bicycles.

Luckily for your uses top-end speed shouldn't be an issue.