Since Shearwater is watching this thread, I will add my perspective as a recreational diving photographer. I use a "two handed" DSLR photo rig. I also dive a hogarthian long hose rig with a clipped off spg, along with my AI computer (Galileo Sol). Having gas info on my wrist is invaluable, as compared to holding my heavy camera rig in one hand, unclipping the spg, checking it, and re-clipping it. That sounds like no big deal but before I hear "equipment solution to a skill problem", try it at 130' in a strong current dealing with the photo rig! In fact, I view AI as a valuable safety factor in that regard, and more than just a convenience. It is a real, tangible, valuable benefit that I desire and why I have not taken the step of buying a Shearwater yet.
As for your other questions, I dont (and don't know anyone and I dive with an advanced crowd including some tech divers) who uses "rock bottom" for rec diving. That being said, my computer allows me to set a "surface reserve" which is the amount of gas that will be in my tank when I reach the surface. It also has a predictive gas usage algorithm, which will tell me to begin my ascent at the pressure which will assure I arrive at the surface with the set reserve, including my predicted gas consumption through the ascent and safety stop. I have found this to be very accurate at least the way Scubapro has implemented it. Thus, my "surface reserve" is the amount of gas available for my buddy if needed during an ascent at the end of a dive. While not as formal as "rock bottom" I can set the reserve at whatever I want, so if I want a cushion, I can set it at 1000, say, on a deep dive. Of course, I will get sent up early by doing this. For dives up to 90' I leave it set for 600, which is enough to get a buddy to the surface in a true emergency OOG situation (which will be faster that usual and not include the safety stop).
If you do "rock bottom" you can set the computer to give a warning at your calculated surfacing pressure or any other turn pressure you want.
As for real time SAC, my remaining gas time is all calculated in real time based on change in tank pressure over time. So, it is, effectively, "real time" SAC calculation during the dive, but translated and displayed as useful information regarding remaining dive time. If you are working hard, the computer automatically takes this into account in its prediction. No mental calculation necessary during the dive.
Such a feature would be essential on any computer I get. I was going to look at the Liquvision Omnix, but posters here have indicated it does not have this feature. That makes it a no-go for me.
My computer also offers buddy air monitoring. My buddy and I can program our computers to read each other's transmitters. A button push during the dive brings up your buddy's gas supply. However, I don't use this much as we usually do a mutual gas check 2 or three times during the dive. Also, because my computer (like most) uses rf transmission, you have to be within 4 or 5 feet of your buddy's transmitter to get the reading from them. So, it is a handy feature, but not necessary.
However, Liquivision uses ultrasonic transmission, which they say is good over pretty long distances, and offers an option to display buddy gas on the main dive screen. This would greatly increase the utility of this feature if it is effective, but I would not trade buddy air monitoring for an effective predictive gas use algorithm.
So, that is my take on why AI is a desirable feature for both basic and advanced rec divers. Hopefully, it offers tech divers some insight into why this feature is so popular and so useful to their rec compadres.
