I started out a few years ago with a Cobra 1 on a HP hose, instead of a console. So I get all the usual console stuff plus deco information. In case the batteries were to die or it would otherwise stop working, I backed up the Cobra with a Suunto D3 bottom timer, so I'd have depth and time for managing my way up.
But then I got to thinking what I would do if Murphy would make my Cobra die while I'm on a dive vacation. That got me to the concept of duplicating it, which I did, in the form of a Vytec wrist computer.
The Vytec replicates everything the Cobra does except pressure, so at this point I was still vulnerable to Murphy's whims. To beat him I had to decide between a mechanical pressure gauge and a pressure transmitter for the Vytec.
Now, you need to know that after my student days I migrated from a jacket BC to a backplate/wing system, and in the new system I found that unclipping and reclipping a pressure gauge was extremely inconvenient and distracting. So I tumbled for the pressure transmitter.
Now I think I have Murphy beaten. In summary, my instrumentation is entirely duplicated: a Cobra 1 on a HP hose, and a Vytec on my wrist with pressure transmitter on a HP port.
Expensive? Yeah, but I consider it as vacation insurance and considerably improved reliability.
PS
A little off-topic, but I moved my console compass to a retractor clipped to a chest D-ring. That lets me get the lubber line EXACTLY lined up, which I couldn't do the old way.