I've had an ALKO Shredder for some 15 years, but blade-sharpening has
always been a pain.
Now that people have been complaining that the blades blunt quickly,
ALKO have brought out
a laser-sharpened version which, being harder, are even more difficult
to sharpen.

Typically of the throw-away business culture, they're not supposed to be
sharpened. You just
chuck 'em and pay around £16 for a new set each time. I'd be interested
if to hear if anyone
has set up a special 'sharpening jig' on a grindstone to accomplish this
task efficiently.