Q: do these actually seal on the jug, and seal up on any airlock? I have some red ones(from another company) that are useless because of this issues.
A: They tighten onto the top of the jug and will accommodate an airlock. They will seal enough to keep pests out.
Q: Will these work with an airlock on the 1 gallon growlers so I can use them as fermenting bottles , or to store and age for not quite finished ferments?
A: Yes the 3/8" hole on the top will accommodate the stem on an airlock