The glass containers are quite sturdy and heavy.
My wife thinks the small is too small to be useful very often.
We kept the cardboard liner to use for storing so they don’t clank.
I’m confused about max heat guidance on the glass - I saw 285 F in the instructions, but 350 F online. 
Also confusing about putting the lids in the microwave, which I wouldn’t do. There’s reference to doing that if you take the vacuum seal off the lid - but the instructions don’t show that, and it looks complicated and fussy to take off and put back on.