I've often wondered this, have a shave and they are fine, go back a few days later and its like shaving with an axe what was a sharp shave previously.
But why do they become blunt ? They are made out of metal and are cutting a few fine soft hair.
Do they become blunt because of exposure to water ?
I do think at £2 a throw for some, this is on purpose, and they add something to the metal to make it corrode quickly after a shave. I mean, if you take a sharp knife and use it to cut a bit of meat, does it suddenly become blunt quickly ?