But you have lost scope of the question. We have a person who is JUST STARTING in the tech world. Not someone who has more gear than some dive shops. We are dealing with someone taking AN/DP and will be on there first set of doubles. Not someone who looses track of how many sets of couples they have. For you, yes I would expect you to have your own analyzer. But for someone who is getting there first set of doubles? And back to the other thing I keep harping on, what analyzer? A basic O2 meter doesn't compare in cost to a trimix analyzer. The question was an analyzer or a Shearwater. Being that a trimix analyzer and a Shearwater are comparable in price that is where I am setting the question at.
SO without getting into what everyone owns, go back and answer the question for the entry level tech diver who is just starting this. Basic entry level here. Not filling there own tanks at home, not pulling out a whip and transfilling on a boat (yet). Good chance the class will be just air and a rich Nitrox stage. And hopefully there will be several dives in this configuration just getting settled in. We all know the eventual answer will be both, and a lot more gear. But properly scale this to what someone taking the class can use right now.
Ask the instructor is still the best answer. Local conditions vary, maybe an analyzer really is needed as there isn't one around that can be trusted or is reasonably accessible. Maybe the instructor like to see a pair of matching computers as a better redundancy.
Remember back a few years to my AM/DP class, and thinking of my local options, I would have picked a second Shearwater. But that was my situation.
She already has a pile of cylinders.
I can also tell you about the club kit which may or may not have had labels removed or been re-analysed when used 32% is topped up with air. In that case the shop might not have an analyser, you might not be present at the fill.
Actually, that is a great example. We regularly dive in Pembrokeshire over a bank holiday weekend. The diving is usually quite shallow and it is a good opportunity to get new divers some experience. The skipper organises the fills. At the end of the day we put cylinders on a big trailer and they turn up magically filled the next day. Sometimes he can do Nitrox, sometimes not. Part of the training for Sports Diver is a nitrox dive, so taking along some cylinders of Nitrox is a good plan. Once those are used they will get an air top, overnight at the hands of the skipper. Analysing that resulting mix is best practice.
It did once happen that I was given a dil cylinder full of oxygen by this process. Fortunately I analysed it before getting on the boat and so had a chance to sort it out.
Analysers are not expensive, you don’t need to be a ‘tech’ diver to think of owning one any more than you need to be a ‘tech’ diver to plan your gas consumption.
If is important to be sure what you are breathing is what you think it is.
Gas logistic errors happen all the time. People really do die from not know8ng the mix in a cylinder.
Primary computer failure fatalities? Not so many.
Best way to spend money, 1/4 the cost on the more likely issue, or the whole cost on the unlikely issue? Hmmm tricky...