I've been using the Personna reds for about 6 weeks and really like them. To start, I just arbitrarily decided to change them every Thursday post-shave for a fresh blade Friday. But, I've wondered, of course, if I was right or wrong. Well, I didn't change the blade this week, and my Friday shave was noticeably sub-standard...no weepers or irritation, but a fair bit of pulling that I hadn't experienced before. So I changed the blade for Saturday and the shave was AMAZING. The pull was absolutely gone, replaced by effortless glide. I'm sure that many change out more frequently, but I know I've found the sweetspot...and that's a great feeling. Cheers!