Not sure about other shops, but both the padi shops(one for confined and classroom, one for o/w portion) my wife and I used for cert last year taught buddy breathing from the same reg as well as the octo. In the pool, we practiced stationary, then an underwater swim together the length of the pool using both an octo and a single reg. O/w we did a single reg share near the bottom (30 fsw) then asended to 15' and held, or tried to as the current was giving us a little ride at the time. Octo ascent was from 30fsw to surface, OOA diver had to inflate b/c manually.