I only use mine once a week but I never had really dark, thick hair and could get away with shaving only a few times a week (or once a week in the winter when no one saw my legs). If anywhere I had dark, thick hair it was my underarms but now that I have been using the epilator for so long, it comes in very sparse, thin, and lighter than before and I only epilate my underarms once a week now. I could probably go a 10 days before I had to but I always do my legs and underarms on the weekend.
I think you will find that after a while you can cut down on the frequency but it might take a year or more before you can do that.