Any HN scuba divers here that would use this as their only dive computer on a dive? I'm not a scuba diver myself but do engage in other adventure sports where reliable equipment can make the difference between a great trip and disaster. I'd be very reluctant to trust my life or health to this.
I'm a recreational diver. I wouldn't use this as my _only_ computer, but I would say the same for the computers I currently use. I always dive with 2 computers just in case one fails, a battery dies, etc. As 'latchkey said, never rely on a single piece of equipment. With that being said, I would be willing to swap out my wrist computer for the Apple Watch Ultra. The superior display and UX would actually be a big quality of life improvement over my current wrist computer. And, I'd still have my backup computer in my SPG to compare against or fall back to.
I think this looks amazing for warm-water vacation divers - typically they are stuck with rental equipment, which usually means a cheap, dated computer on a bulky console. Having a well-designed UI will definitely improve these divers safety - the last boat dive I went on, an experienced diver blew past no-deco limits because he didn't understand his unfamiliar rental computer.
That being said, I can't personally imagine taking the Apple Watch Ultra to, say, 80-90 feet if it's only rated to 130. It's just too expensive.
Slight clarification: the Apple Watch Ultra has a water resistance rating of 100m. The Oceanic+ app has a 130ft/40m limit because that's the recreational diving limit.