We carried something like these offshore out of Eastern Canada (pax and crew);
Main Catalog > ?Emergency Breathing Systems (EBS) > Survival Egress Air (SEA)
Having the separate mouthpiece is much easier, and you have both hands free for escape. The bottle mounted on the vest/survival suit and the mouthpiece was up by the mouth. The valve was left open in flight, so all you had to do was put the mouthpiece in and breath in the event of a ditching. Easy to find too if you were in the water prior to knowing you needed it. We trained with the bottles every two years in the dunkers.