£5.99 divided by 15 weeks of shaving x 52 weeks a year = £20.76 for a year's worth of double edged razor blades.
That's a saving of around £31 a year and less than half the cost of shaving with Mach3s.
Even in the first year, where you would have to purchase a double edged razor, this saving is more than enough to cover this initial extra cost.
Dan at The Shaving Shack's story
I am one of the lucky ones who can get away with using one DE blade a week so my yearly costs are now miniscule. Also, although I don't have very sensitive skin, I used to get a red rash under my chin after using a Mach3. After about a month of using a DE the rash disappeared. We get a lot of sensitive skin sufferers whose skin does not take kindly to having 3-4 blades pass across it. After switching to a DE, they generally notice that the irritation is lessened or disappears entirely.