re: Scuba Diving computer/watch question?

Why?
Because the watches and tables are not reliable while the computers more accurately calculate all of your time at varied depths rather than a simple theoretical version of deepest point.
Your computer also calculates your surface interval so that your tired and confused brain does not make an error which could be a serious problem for you if you go back under the water too soon.
I have seen people make errors with tables and watches. I helped them by showing them my computer and convincing them to correct their errors.
I suggest a computer if you are a serious diver.
From there, the question is who makes the best wrist or gauge mounted computer.
Sadly, my information is dated since my equipment is old, so I will avoid making a recommendation for current sources.
I actually had 2 computers and a good dive watch when I lived where I could shore dive any time that I liked.