I started using the Doidy when my baby was 5 months old. It is such a simple cup - no lids to faff around with, simple to wash etc. It took a few tries before my baby could drink and swallow some water but she seemed to get the idea quite quickly. At 8 months she still hasn't mastered holding it - if she does get her hands on it, it's to turn it upside down so I hold it for her. I've tried three other styles of training cup and the Doidy is certainly the easiest to use at home. For out and about I use a simple lidded spout cup.
The option of a lid to fix on would be handy for outside the home - if Bickiepegs want to make an improvement! Then I'd give it 5 stars.