The last Mach3 blades I clipped on sit there for almost 2 years now. Still shaving fine. Are the blades dull? Undoubtedly. Do I notice that? Not at all. The only time I have small cuts on my face is just after I start using a new blade.

PS. The blades have this psychological marketing trick of the blue indicator bar, where once it is worn away it is supposedly time to get new blades. Just ignore and use as long as it shaves. Your mileage may vary compared to me, but I'm still getting rid of quite heavy-duty stubbles without issue.