My thoughts on dive watch/instrumentation/computers has changed as I have become more experienced in hyperbaric medicine. Having been on two recent trips where one diver had some signs and symptoms of decompression sickness (DCS) that required a visit to the hyperbaric oxygen chamber and another diver who had DCS or an arterial gas embolus (AGE) that required 14+ chamber treatments and an air med evacuation to Duke. Both of these two divers were experienced with well over 1500 dives between them.
Dive tables with repetitive dives are not as accurate as a dive computer, so if your computer fails and you go to tables you are at a disadvantage.
A second computer that is the size of a wrist watch and also is a watch adds a further margin of safety.
Thatt's what I do.
But after both computers and the backup batteries for them fail, then you are going to need your dive watch.