Does this matter for a casual recreational dive? Is a console really that much more drag than a gauge?
Wow! I completely missed how they are sold separately. This option is out of my price range, at least unless I buy used.
There is nothing magic about dive computers (or any computers). And if it were difficult, you wouldn't have thousands of different choices for essentially the same product. The only thing special about a dive computer is the hardware to sense depth. Everything else could be easily done with an Arduino or Raspberry PI, although manufactures are using smaller, cheaper, proprietary waterproof hardware which is going to be a little harder to work with but really the same process. I don't see the point, if I come up with a remarkably better idea for how to design a dive computer, I will patent it and sell it, not make anything just for personal use.