I used these size 1's up until 6 months and am now using some size 2's alongside the 2 part bamboos.
My baby is in the 75th percentile size wise in comparison to other babies, so size 1 will probably go longer for other babes.
The bamboo insert is what makes these so good though. It's very absorbent and easy to use. I have to use the insert as well as a booster (any thickness) to last a couple of hours.
I've given 4 not 5 stars only because my baby will outgrow size 2's before she's out of nappies. But I really enjoy using these and not disposables regardless. It feels great washing everything!
For size see pictures as there's one with size 1 on size 2 for comparison:)