Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.
Benefits of registering include
Ability to post and comment on topics and discussions.
A Free photo gallery to share your dive photos with the world.
Thanks everyone for the welcoming and very insightful replies, much appreciated!
For those who asked, no, the operators here typically do not require a redundant air source, so it's definitely optional. I do lean towards those saying "better safe than sorry" essentially, it would probably give me more peace of mind / confidence to have something available "just in case". I'll have to weigh this against convenience and practicality much in the same way @SlugMug already outlined, as it sounds like either a 19cu or 40cu pony bottle would probably be the most straightforward way to go. I'm going to investigate some options and cost!
If it’s gear you meant, AL40! Sling it. Good for if you go tech later. Will hold its value if you decide to sell. Tech divers are always looking for more AL40s. I always did the pony when I was doing wrecks deeper than 60.