I agree with
@scubadada. The Aqualung looks very much like an Oceanic OCi, to me. Very similar to the Oceanic Atom 3.1. But, the Atom (and OCi, I believe) has two algorithms, DSAT and PZ+. The Aqualung only has PZ+. Of the two, I would definitely buy the one with DSAT. I have been using an Atom 3.0 for over a year and a half, always on DSAT. I like it a LOT. DSAT will give you longer NDL times than PZ+ and longer than most of the RGBM-based computers. Generally. There may be specific situations where that is not true, but I do believe it is true for the vast majority of ordinary recreational dives.
And keep in mind, you can always choose to end a dive early on a liberal computer, but (if you follow your training) you cannot stay down longer when you're using a conservative computer that says you have reached your NDL. You can also set the Conservatism Factor up from the default, on a liberal computer, if you want it to direct you to ascend at a more conservative time, instead of having to guess for yourself how much to pad your NDL.
All of that about algorithms and conservative vs liberal NDL MAY not matter to you. If you're always diving an AL80, and you don't dive enough to get really comfortable and lower your gas consumption rate, and if you generally dive shallower dives, then you will probably run low on gas before you hit your NDL - in which case the algorithm won't make much difference to you. But, I've found it pretty easy to rent bigger tanks when I want them. And it only took me about 30'ish dives to get my gas consumption down to a level where, at least on deeper dives (100 foot range), I had no trouble at all getting my gas to last longer than my NDL - on a very liberal computer, and even on Nitrox.
I disagree somewhat with Captain Sinbad in that I don't think having AI automatically makes you a diver who is going to focus on bells and whistles to the detriment of enjoying your dive.
For ME, the AI on my Atom 3.1 makes it easier for me to forget about bells and whistles and enjoy my dive precisely because I was one place to look for all the info I need - instead of 2 or more - and it's very conveniently located on my wrist. AFTER my dive, I do also value being able to download my dive data, that includes my gas consumption, and review it in Subsurface (a free dive log application for Windows, MacOS, and Linux). Without AI, I could calculate my gas consumption average over the whole dive. With AI, I can see my average over the whole dive but I can also see the instantaneous consumption rate during any part of the dive. I can see that my average is 0.55 cu-ft/min, but at the very start I'm using 0.7, when I'm swimming along the bottom, I'm using 0.7, when I'm just drifting along, I'm using 0.45. When I'm hanging out at my safety stop, I'm using 0.4. I think that information is interesting and helpful in planning future dives.
From my somewhat limited (just under 2 years) time of watching ScubaBoard and the computer Classifieds, in particular, I'd say there are two reasons that are the most common ones for people to be selling their computers. One, they are going tech and want a tech-capable computer. And two, they have found their computer to be too limiting on dive times because the algorithm was more conservative than what the people around them were using.
Yes, there are a lot of other reasons I've seen for people selling their computer. Those just seem to be the two most common ones. In contrast, I have never seen anyone selling a recreational computer in order to replace it with another recreational computer because their old computer didn't support enough gases. I think multi-gas support on a rec computer is marketing fluff and not a factor to ever be considered in a recreational computer purchase. They pretty much all support Nitrox. Some support Nitrox to 40%. Some to 50%. Some to 99%. I have never seen anyone selling a rec computer in order to replace it with another rec computer that supports a higher percent of oxygen in their Nitrox. Rec diving only uses up to 40% Nitrox anyway. Anything more than that is tech diving. So, as long as it supports Nitrox, the specific percent is also not a factor in a purchase decision.
So, personally, I'd say that if you want AI and you are not interested in pursuing tech diving, then you should prioritize having AI, Nitrox support (which they all have now), getting the size/form factor you will be happy with, and getting something with an algorithm that you won't find limiting and want to replace later. But that's just my $0.02.
