> Nobody replaces their Mach 3 cartridge after every other shave but that's a common recommendation for DE blades.Yeah, but you can buy a box of 100 DE blades for, like, $15. (Seriously: see https://www.westcoastshaving.com/collections/bulk-de-safety-...) So even if you change the blade every other shave, it still comes out cheaper.
This is a benefit of standardization: DE blades all have a common form factor, so any handle can use any blade. That means every DE blade maker is competing with all the others, which drives prices down. Cartridges on the other hand are all proprietary to the vendor that made the handle they fit with, so there's much less downward pressure on the pricing.
> if that isn't a strong indictment of saving pennies, I don't know what is.
The thing about a DE blade versus a cartridge is that with a DE the range of possible outcomes is much wider than it is with a cartridge. A DE blade can produce shaves ranging from "ow, I cut myself!" to "smooth as a baby's bottom", depending on the technique you apply to it. A cartridge won't ever cut you, but it'll also never give you as close a shave as you can get with a well-wielded DE blade; it provides a consistently mediocre shave every time.
To put this in terms HN readers will appreciate, arguments about DE versus cartridge tend to be kind of like arguments about vim/emacs versus IDEs. Vim and emacs users love to talk about all the crazy things they can do with their editor that no IDE can match, but they rarely talk about the learning curve they had to climb to reach that level of technique. Whereas IDEs tend to be less elegant, but by hewing more closely to modern desktop interface standards they let their users reach an acceptable level of productivity faster. Those IDE users will never reach the heights of wizardry that are possible with vim or emacs, but since very few programmers are true wizards anyway that doesn't really matter much to everyone else. Like the cartridge razor, the IDE is "good enough."