The description says they have tiny holes in the lid to relieve pressure. I filled one with water, seated the lid, and turned it over on a facial tissue. A tiny amount of water leaked, perhaps as much as one drop. Then they remained continent all night. A very aromatic fluid might leak and leave some scent in whatever I'm carrying the bowl in, but this generally seems capable of carrying wet foods for work, etc.
I filled them to near the top with water, but allowed some expansion space, and then froze them without the lids on. The ice expanded upwards and did not distort the bowl. Then I put the lids on (2 of them) and packed an empty one between in the neoprene bag and left it on the counter. The ice lasted about 4 hours.
The elastomer seals are silicon "rubber" - which isn't rubber, isn't plastic, and is generally non-toxic and long lived. The elastomer will be damaged by a fire or sufficient heat, but the bowl can be cooked in. The lid (with elastomer) can be used as a bowl for convenience, e.g. put your chips in it to dip into the bowl with the guacamole. The lid will hold liquid as a cup, but see above and try it yourself.
I bought these so I can avoid using plastic for lunches, food storage. I may find camping uses for them as well (uh... such as lunch or food storage). I don't yet know how the bowl will handle heat - but it doesn't seem flimsy.
I'm pleased with them - I find they do what the maker says they will.