I bought the first one looking for a good leftover container my husband could take to work. The one he had been using was so stained and who knows how old. What drew me to this brand was that it claimed it would heat without staining.
I like that they are clear, easy to stack and there is absolutely no staining. Oh and they are guaranteed for life. As for cost, it's not too bad. And they usually go on sale frequently. I even used a coupon when I first purchased a set.
We have two sets of these of the various sizes. I use the 1 cup size for storing and freezing individual sauces. We store cheese in one almost all the time. Sometimes I go to reach for one and there are all in use.
If you haven't tried these containers and are searching for some good ones, these are worth trying!