The cup is absolutely tight, if you assemble it correctly, filled with water and upside down. However, if a baby gets this cup in your fingers, you can no longer speak of tightness. Our daughter has taken the cup often up at the edge, which leads necessarily mean that the valve is pushed down and therefore the water has run wild.
Anyway some water under the valve remains, which then runs out the case of overturning of the cup.
Furthermore, the valve of the top and bottom about ends with the cup rim and toward the center about 0.5 cm below the rim. When the cup is filled to the brim and you have to hold it for drinking horizontal, the child pushes the nose of the valve, presses down there, and the water already flowing out before the lips have ever touched the cup.
Positive in the cup, the handholds, the lids are (although I can not tell if he actually tight stops) and the fact that you can clean it in the dishwasher, sterilized in the sterilizer and plug (without handle and valve) in the microwave can.
ADDENDUM: I now have even ordered the cup of NUK, which corresponds almost exactly to my expectations ...
NUK Magic Cup 250 ml, novel drinking rim, sealing silicone disc, from 8 months, made of polypropylene
