I've been using the 0 and 3 for a year and my hair is definitely a little bit stronger. Not massively but it has made a difference. I use the no.6 for styling and like it too. Do any of you rate the no. 4 and 5? Are they worth getting? I have v v thin hair that's brittle and dry (well a bit less so now). If it's worth the money I'll invest. Would be interested to know what anyone thinks about it.