If getting the maximum bottom time is your primary criteria
I agree ... so other than the computer's algorithm, what other criteria do you think should be considered?
... Bob (Grateful Diver)
You'll notice, if you look at all my posts in this thread, I never recommended a computer. I also never said maximizing bottom time should be a top priority or primary criteria.
I simply said that when someone buys a new computer that is a characteristic of the computer that they should understand. I also said that a common reason I've seen for computers for sale in the Classifieds that are relatively new and/or have relatively few dives on them is that they are too conservative.
As for criteria that should be considered...
I find all this talk about algorithms a bit too much getting into the weeds, particularly for a novice diver who is going to be more limited by available gas supply than NDLs. I think pretty much any choice of dive computer is going to provide a safe algorithm for recreational diving, and that the whole issue of "conservative" algorithms is essentially overblown. If it's a concern, many computers nowadays come with a setting you can use to change the conservatism of the computer ... although there's a caveat there as well which is that before changing the default conservatism you should have some idea (through experience) of how it's going to affect your physiology ... and what factors might cause you to want to dive a bit more conservatively on any given day.
What a newer diver really should focus on purchasing is a computer that's easy to read, easy to set, and intuitive to understand what the numbers being displayed during the dive are telling you. And for almost all of us, getting one that's EAN compatible is important ... even if you don't currently use nitrox, because at some point if you should decide to you then won't have to purchase a new computer.
I agree that being easy to read, set, and intuitive to understand the numbers are all good. But, I think understanding the algorithm is equally important. Also, your statement that "many computers nowadays come with a setting you can use to change the conservatism" is incomplete and, thereby, misleading. With no further information, the reader would be left to believe that they can make a computer more conservative or less conservative and that is not true. All the recreational computers I know of come with a setting that only allows you to make them MORE conservative. If you buy a Zoop and it turns out to be more conservative than you would prefer, there is no setting you can change to make it less conservative.
Really, if I were to tell a new diver what criteria should be considered, I would say:
algorithm (not to be taken as a recommendation for liberal - only a recommendation to understand what you are choosing)
readability - to include that an OLED or LED display will be much more readable in low viz conditions than an ordinary LCD, but some OLEDs are really hard to read in bright ambient light conditions
mounting location - consider whether you want a console, wrist puck, or wrist watch
air integration - consider whether you want it or not. I feel like (anecdotal) another common reason for people to replace computers prematurely is a desire have air integration
Nitrox - should absolutely be supported, but not a factor except for older computers
Trimix - Recreational trimix seems to be becoming more common. Before buying a computer, the diver should probably evaluate their agency, instructor, and where they dive to figure out if trimix is in their remotely near future. If it is, they should definitely factor that into their computer purchase. Not many computers support trimix
Battery - coin? AA? Built-in rechargeable? User replaceable? Proprietary? How long will it run on a charge/fresh battery?
Tech - the diver should consider whether tech training might ever be in their future. If they think it might, and if they have the budget, I would suggest a Perdix above all others. Either a good used one, or a new Perdix AI. Buying a new Perdix (non-AI) does not make financial sense (to me). The user market has numerous, for cheap, and the Shearwater warranty is transferable. And even if they don't think tech training is in their future, the Perdix is still an excellent choice to consider.
And I would specifically add to NOT worry about:
multi-gas support
support for O2 over 40%
Even the less expensive computers are not cheap. I think buying a dive computer is a serious purchase that merits serious consideration and taking plenty of time to understand all the criteria I listed, then making an informed choice. There are lots of people that post about still diving computers they bought 20 or more years ago. If someone asks me for advice on buying a computer, I would try to help them arrive at a decision that they can have some hope of still being happy with in 20 years - not just for the next 6 months or a year. And if a person keeps diving for 20 years, I would think there's a good chance the algorithm will become important to them at some point during that time.