This is a well-designed, easy to use product.  Glass allows any food items to be refrigerated or frozen and then heated without having to transfer the food to another container.  The size is great since it will fit into the refrigerator in narrower spaces than wider, square containers.  The seal is very tight and easy to use with just a push to make the closure work.  I found that it is best to work the opposite side seals rather than working around the container, one side at a time.  Once the seal is properly seated by closing the opposite flaps, the other two snap quickly into place.