The Move or Roan would be a much better option for travelling as it was designed to work outside of your wifi network (or plugged in).  While the Era 300 does have an external bluetooth switch, I am not 100% sure it will work as a standalone bluetooth speaker while not connected to WiFi. The Move and Roam will automatically tune to whereever it is placed, while the Era 300 will not. Sonos portables are also dropped and tested and designed to handle the elements better.

Thank you, Danny,  that is about what I have thought. I am asking, though, about very occasional use for traaveling, maybe two weeks a year. I am looking to upgrade a home speaker and wondered if it would work for an occasional trip rather than buying an additional portable speaker such as the Roam or Move.

I’ve not tested this, but my understanding is that you’d want it connected to a WiFi signal of some kind. I’d go with a travel router, since I already own one, but concur with @melvimbe that I wouldn’t expect Bluetooth to work without an Ethernet connection, since Sonos doesn’t advertise it as such. 

The 300 probably would work, you might have to do some tweaking or use a travel-router at some point.

The big sticking point for me is that the Era-300 is likely to get beat up and ugly in short order. Maybe if you kept the factory packing to transport it you’d be good.