But does that contraption keep it fresher than sealed in your fridge with a lid?
It keeps it fresh once opened, so, yes. Once a growler is opened it must be consumed during that day. This will allow me to have multiple growlers "opened" which mean I can consume different growlers (different beers) all at the same time across multiple days. It is essentially a multiple-keg-kegerator on a small scale. Considering the limited degree of consumption, on my end, I believe this serves a great function in my experience of craft brew imbibing.