[ashtonbaker]

That sounds like overkill CYA from the legal department. Diving with two computers is not standard protocol in no-decompression recreational diving. It is in technical diving. But if you're in open water, and within no-deco limits, if your computer fails, you can always just end the dive.

[isitmadeofglass]

As I recall PADI recommendations is to have a backup plan equivalent to the primary plan. Which often is easiest with redundant devices and each buddy having the same or similar computer.

I think it’s very much not recommended to have going computerless as a backup. And the idea that you are safe to do so because your “within no-deco limits” is potentially dangerous, as your relying on the computer to tell you if you are still within that limit.

Many people go quite close to the limit. Personally I stay far away from them, but safety recommendations are the same for everyone.

[ashtonbaker]

I think you're saying that PADI's recommendation that "you should have a backup plan" means implicitly that you should dive with two computers. They wouldn't make that an implicit recommendation, they would make it an explicit one. Which they do not. At least not for open water recreational diving.

The backup plan for recreational open water diving would typically be to end the dive if your computer fails, not to continue computerless. At the point that your computer failed, you should have been within no-deco limits, which you can confirm with your partner's computer to a reasonable margin of safety, so you can ascend safely.