Twinplex Stropper Razor Sharpener

Q: I paid 50 cents at a yard sale for a metal contraption that the seller thought was a pencil sharpener. When I took it out of its box and found the original directions, I figured out that it was a razor-blade sharpener. If you put a double-edged razor blade inside and turned the crank 15 to 60 times, it sharpened both sides of a double-edged blade. The paperwork in the box calls the sharpener a Twinplex Stropper and says it was marketed by the Twinplex Sales Co. of St. Louis. The patent dates on it run from 1915 to 1920, and the original price was $5. I was wondering why this invention didn’t catch on and what it’s worth.