Ellis is 7 and a half months but i got the cup when she was about 4-5 months, she's bf and wasn't too keen on taking a bottle. The doidy cup does take some practice and to start with she'd seem like she had overfilled herself and spluttered a bit but now she's really good and seems to take as much as she wants. I have two sippy cups, one from the dentist which is free flow (to ensure supervision when/if Ellis is given juice-Ellis is part of the child smile program) and a tommee tippee one which had a flow regulator but Ellis was pretty rubbish with it and chewed it more than sucked it.
I don't give her much water as she's still bf on demand but if her meal is a bit dry-toast,lentils,mash etc she likes a little drink and its pretty obvious when she wants one.