The plastic lid of the container close to its "Clip and Close" mechanism easily, quickly and firmly. Even the glass makes a high-quality impression, especially created here in the long run not stain like plastic dishes.
The three sizes, I personally find good. To work I usually take the biggest tray, the average is for small portions too, otherwise for meats or cheese in the refrigerator. The very little I use then rather for storing capers, homemade pesto, etc. It should be informed in advance about the included variables, because if you but uses only one of the shells, then the set appear less favorable.
A nice side effect is the variable use of glass bowls as baking dish and the ability to store them in the freezer. The cleaning also makes hardly working, so for me there is no deduction.