Everybody is different when it comes to how long a DE blade will last them. I am pushing it to get past 5 uses without an ugly feeling blade. A friend of mine "says" he goes 3 months with the same cart head.
Bob
Does he shave 4 times a year? On a serious note they would last me quite a while, I shaved probably 3 times in 2 weeks though, and the head was always clogged up.