I really like these cups. I now have 3 of them, and have ditched my other sippy cups. But they are not 100% perfect.
PROS
1. The teat folds down, so it is much easier than dealing with a cup & lid.
2. It is also very easy to clean.
3. It does not have a valve, so it encourages sipping rather than sucking (dentists prefer this)
CONS
1. The flow is quite fast, so my son was 10 months (not 4 months) when got the hang of it at 10 months.
2. Some batches seem to have tighter lids (2 of my cups are fine, the other I really struggle to get the lid off!)
3. It is pretty much impossible for the baby to get the last 15mls out, therefore there's wastage unless you remove the lid.