Using medical O2 for aviation is akin to using a vet for your health care, wrong application. The vet might just shoot you for a broken leg.

There is absolutely NO DIFFERENCE between medical, aviators or welding oxygen. Moisture may be introduced at the delivery device for medical applications, but in the cylinder itself, they are all 99.99% O2. Any moisture in the pressurized cylinder, in the presence of an oxidizer (O2, get it?) promotes corrosion of the aluminum or steel cylinder.

I wonder how long this fairy tale about the "differences" in oxygen will survive?