Funny I am referring to recreational diving.
I use to dive with a 19, then went to a 30 and now with a 40.
A 19 is useless diving deeper that 80 feet with an insta buddy. Risk is to great in my opinion. I use to dive that way and found out the hard way it was not enough for two divers especially when one of them is an air sucking hog. I was DMing an advance course adn both divers I was paired with, sucked back an 80 in no time and were narced up the ying yang...and we were on the deep dive portion of the course. I handed my 19 to one and gave my octo to the other( I had twin 80's)...the 19 was almost dry when we got to a safety stop...called over the other DM to lend an octo...for me lessened learned.
I stick to recreational limits with instabuddies..and always dive a 40 - not for me but for them in the event of a low air situation.
Anything lower than 80 feet, you need to rethiink your gas management. Even though it is for your own safety. You do have a buddy to consider regardless if he /she is an insta buddy or not. Proper gas management. Which many recreational divers never think about is vital, especially if they venture deeper than 80 feet.
So why not add a greater margin of safety, when diving deeper than 60 feet....
A 19 can be a good size for shallow diving. Which I am not disagreeing upon. My point is - a 19 at depths greater that 80 feet is not the right tool for that depth. This is based on my experience and those I dive with. In the conditions I dive in.
you dive your dives as long as they are all safe dives.
So when someones asks an opinion on something, do expect a varied array of them. Take what you want from them..but do not knock the opinion of others. Especially if it is based on experience.
Enjoy.
Maybe for you, but for recreational divers a 40 cft bailout bottle is far larger than necessary. 19 cft of air is plenty for any recreational situation. If you truly NEED more air as a bailout in recreational diving, I would venture a strong guess that you're doing something very wrong in planning/profile management. You might WANT more for your own reasons, but saying anything less than 40 is useless is not an accurate statement at all.
The vast majority of recreational divers consider it perfectly safe to dive with a 750PSI reserve, which is just about 19cft of an AL80.
Tech/deco/overhead diving, totally different scenario.