I've been using the disposable cartridges for many years, but in practice they do last me a fairly long time -- between the fact that I'm only shaving part of my face, and that I've never been one to reliably shave every day (even before I started working from home ten years ago), I usually get well over a month from each. A package from Costco lasts me a couple of years.

So as waste goes, they're a relatively minor sin for me personally -- not nothing, but not one of the things I've actively tried to change my habits over yet.