I use one for my under arms.
I don't use disposables any more. I'm with Corey and also use the Gillette Fusion. Best shave I've ever had.
I think I read an article that said anything over 3 blades doesn't effect the performance one bit. The problem is finding one that isn't too cheaply made.
I have light facial hair, so a disposable will last me for a month. I think the current bag has three blades. Used to use a regular razor, but then the blade companies started switching to "shaving systems" and I couldn't find snap in cartridges for my old razor anymore. And I am NOT buying a "system" to shave with.