Method seems plausible. As OP mentions, it requires a bit of work on a daily basis (especially at the start) with some hope/chance of automating the process.
Personally, the work involved (despite not being overly difficult) won’t be worthwhile for everyone. On the surface it looks a little tedious, but if you’ve got free time and want to earn a little on the side without laying out any capital (other than the method purchase cost) then this could be useful for you.
All in all, I guess it depends mostly on your position and schedule to see whether or not it’s worthwhile. There are plenty of other ways one could spend the same amount of time to get similar profit margins.