About two years ago I got well and truly peed off with the prices of said products so did a search to find a way to sharpen them at home.
I take no credit for the two methods other than saying they do work as I haven't bought new ones since I started using them.
Methods:
1) Rub the blades against a piece of Denim or similar, opposite to the opposite to normal direction of course.
Works the quickest on dull blades.
2) Ditto against body hair, arms and legs, and act like strops.
Geoff – Waiting in anticipation