Yup...what CHFather said. I always had an M tank for home...and a buncha e-tanks for out and about....AND peace of mind.
Each needs it's own regulator...again...on the internet not too expensive. Some O2 shops "require" you to rent these regulators....tis ridiculous...buy yur own. A nonrebreather mask is not just a good idea...its the ONLY idea...don't let 'em give you nasal cannulas or a regular mask with holes....
I like the idea re educating the O2 shop...in my experience it was the manager (smooze 'em...get to know them...put a face to your patientness) of the shop who was (or not) interested. Met both kinds...the "don't giva damn"...and the "wow, that's cool, thanks, I can use that for my other ch patients"...so give it a go.........
....and yeah...we are a special group...clusterheads are "clusterfukked"... so we look out for each other......
Best
Jon