From what I've read, people like Shearwater because:
1) They're reliable;
2) Tech divers don't like air integration - it's a potential point of failure;
3) Some rec divers also think air integration in its current incarnation is unreliable;
4) Big, easy to read screen;
5) User replaceable batteries;
6) Nice straps/bungee;
7) Company provides good service;
8) I'm sure there are other reasons.
Both my husband and I have one. We are beginner recreational divers.
2: right now it is more because they are big and expensive. Most of us are cheapskates and while we have no problem spending a lot of money on something if it is worth it, WAI just isn't. Current cost right now for transmitters is about 6x that of a SPG and hose. Most of us only look at our SPG's 2-3x throughout the dive, so it isn't worth it.
7: I don't think good really begins to describe their service.... It is truly legendary in this industry....
the biggest thing right now is that in the US, which
@KenGordon at least has access to OSTC, they are really the only technical diving computer really worth purchasing if you want a high end one. Yes they are about $100 more expensive than they were last year because the Canadian Dollar is quite a bit more stable than it was, but they are still a bargain compared to the other options out there. There are plenty that are more expensive, but none of them worth the price increase. There are plenty that are cheaper, but you sacrifice a lot of features that may be worthwhile to you.
WAI is coming, maybe not from Shearwater *the last official statement from them said it wasn't in development and wasn't on the plan for development*, but it will come to technical diving. No one has build a cost effective WAI solution, and no one has built one that really works well with LOTS of transmitters. My last OC cave dive I would have required the computer to behave with 7 wireless transmitters, and none of them can do that reliably. I think the Suunto Eon Steel is the only one that can think about it. Instead of $850 for the Perdix/Petrel and $500 for 7x SPG's and hoses, I would have had to spend $1140 *black friday sale price* for the computer, plus 7*$440=$3080 for the WAI transmmitters. You want to spend $1400 or $4200 to watch your gas? On top of that the Eon Steel really isn't a sufficient technical diving computer due to the algorithm it use. It does have a really nice planning tool built into the software and that is something that Shearwater is seriously lacking in right now, but so is everyone else in the industry so it's not like you are "losing out" against another manufacturer.