A mach3 blades lasts me about a week and a half to two weeks and I shave daily, but this is probably cause I shave in the shower so my face is really moist when I do so. Mach3 is one of the greatest human inventions. Using this razor for over 2 years now and there has NEVER been a cut, NEVER been any irritations at ALL, and my skin has never felt dry or stretched or anything else like that. I'm gonna have to give these new blades a whirl.
BTW I use it with Gillette Shaving Gel (for sensitive skin kind), you only need to use a tiny tiny bit of it or else you just waste half of it on your hands. Typically a bottle lasts a month and I usually pay $3.50CDN a bottle or less if I buy it in 3-packs at costco or something.