I use it all the time, and it works great with no trouble for a year now. At 19k you need to do 8 or 10 chains a day, and charge what it is worth, which I feel is more than 5 donuts. 10 chains a day at 7 is 70, times 5 days a week, 350, times say 50 weeks a year, 17,200, so it will pay off in just over a year.
However, if a tech is sharpening chain now, is he making shop labor rate? At 5 per chain? Probably not. So with the Franzen and someone other than a tech running it, like maybe the parts guy, then the tech is on the bench doing billable hours at shop labor rate, so if you add that in it will pay for itself in a year. And once you learn how to use it, it is fast and consistent, so the customer will be pleased with the job.