I prefer an air integrated computer because it provides all of the relevant information in an easy to read format. Rather than looking at individual SPG, depth gauge, and bottom timer, I can look at the Cobra and get all of the details, thus reducing task loading. A computer is not a good substitute for training and planning. It shouldnt be a shortcut. In fact, if used correctly a computer requires more knowledge than a traditional SPG, depth gauge, and bottom timer, because you need to understand how the computer works and how to configure it.
IMO relying on computer calculated remaining air time calculations is no more dangerous than diving with an SPG and the only plan being to be back on the boat with 500 psi. Yet that appears to be commonly taught and practiced. I wouldnt do either. In any case, you should have a dive plan that budgets both gas and NDL with turn points (if appropriate) and ascent points for both. With that being said, I think that the estimated air time is useful tool for determining the optimal depth (where remaining air time equals remaining NDL time) on a multilevel dive such as a wreck.
Also in my opinion, allowing the computer to calculate remaining NDL time is inherently safer than calculating it your self, especially on a multilevel dive, since it reduces the possibility of human error.
Mike