I use the Gillette Fusion. I shave every other day, head only, and change the cartridge monthly. So that is an average of around 15 head shaves per cartridge. At the end of the month I am still getting good shaves, but it does drag a bit. I don't really notice the drag until I shave with the new cartridge, so it is not that bad. So I could extend the use even longer. In addition to my head, I also do a little cheek line shaving on my beard.
FYI - I shave in the shower and use Cremo brand shave cream. The shower keeps my head moist throughout the save. I store the razor on the upper ledge of the shower, up side down, so the blades dry well. Also, my financial situation is good, and the cost of the Fusion cartridges does not bother me. I have used other types of razors in the past, and for me, the Fusion is the best I have used and lasts the longest. I remember changing cartridges weekly on some of the cheaper brands in the past, so they actually cost more to use.
