Dive computers can be a bit of a religious issue, particularly when it comes to AI. I absolutely love AI and won't do without it. Many opt to have their SPG in a position that can easily be seen with a quick glance down. But, that doesn't work so well if you are diving at night (which I love) or you dive in dark waters (like I dive in the Pacific Northwest) as you have to shine a light on it. I'd rather not have to do this. Since I'm often task loaded with shooting a large camera setup, I like to keep track of my gas supply with a glance to a bright OLED screen on my wrist.
Now some will surely criticize me for what I'm about to say.
When I am not in training dives and I'm diving a tec setup/doubles, I attach my transmitter to my right post. I love AI and it is that simple. Some will say that AI fails with losing a link. It all depends on which dive computer you have. I purchased the Aeris A300 CS as soon as it came out. There were a number of manufacturing issues. I'm on my fourth one now I believe. Now it is solid as a rock. Never loses connection. The only issue that I have is that the battery life is poor. So I have a number of rechargeable batteries. The latest firmware warns if the battery is low, so I can easily swap batteries when I'm back on the boat/shore.
Just something to think about.
With regards to dealing with OOA divers, the few recreational divers with whom I've spoken to who have had to deal with that, all of them had their regs ripped out of their mouths, so I question the usefulness of the long hose for that scenario. Maybe it has happened, where an OOA diver signaled "OOA" and then "share air" and the donor either handed them a reg or showed where the receiver would grab it. But I'm guessing not that often. For my vacation setup, I do have an Air2 to be more streamlined, though in a bit of contradiction, I do always have a pony bottle (which introduces drag), as usually taking pictures, I'm essentially diving solo.
Hopefully you'll find divers with varied configurations who are willing to share their equipment with you (yes, I know that there is a liability issue in doing such) so that you can get a feel of what you really want. There are so many options that can be overwhelming.
If anyone mentioned dive lights, I've missed it. I really love Big Blue for the price/performance ratio.
Scuba diving is like crack. Once addicted, you'll be spending a lot of money to support your habit as you venture into different types of diving. I do agree that when it comes to regs, spending money upfront is a good idea. I have 6 regs: 2 ScubaPro MK25/S600's on my doubles, 1 IST (forget which one), 2 Apex XTX50's for my single tank setup, 1 ScubaPro MK11 and I forget what 2nd stage for an oxygen clean deco bottle. The MK25/S600 breathes so incredibly easily compared to the IST (on a 30 cu ft pony/deco bottle), and slightly better than the Apex regulators. I find that this helps me relax and thus helps with lowering my SAC. With teaching, I have full setups so I can quickly switch from one kind of diving to another. Eventually I'll get a nice sidemount setup, as when I travel and want to do longer/deeper dives, I can be using 2 AL80 tanks.
I hope that something in my rambling is useful to you.
