MDW - 9/26/2017 11:44 AM
I know I’m late to the game, but here’s my 2 cents.

I would go with a simple brass and glass SPG, a wrist mounted compass, and the cheapest backup computer you can find with gauge-only mode. This will be your least expensive and most flexible and future-proof option.

Here’s why. A simple SPG will work with any regulator, almost never fails, and costs about $50. It’s low profile, won’t get snagged on stuff, and as a single function standalone device can be left clipped off except when actually checking your pressure. A wrist mounted compass is always there in your line of sight or peripheral vision for quick consultation and can be easily moved to the back of the hand or held in the hand to get it perfectly aligned in front of you without the hindrance of 2 other gauges and a hose attached to it. Likewise, having a wrist mount backup computer on the opposite arm as your primary puts your depth and time information in easy view without having to hold anything in your hand. Running it in gauge mode prevents having 2 computers with conflicting NDL or deco info and allows you to either take or leave the backup on any particular dive (if running in computer mode you can’t leave it on one dive and then use it on the next because it won’t "know" about your first dive). In gauge mode, it is basically a depth gauge and a watch, which can be used in conjunction with tables to backup your computer. A cheap computer in gauge mode should only run $100 or so.

I choose to run the following:
Primary computer (which has an electronic compass function) on my right arm - this is my backup compass as well
Compass and backup computer (gauge mode) on left arm
Simple SPG clipped to left waist ring (backmount) or simple SPG on short hose on each tank (sidemount or stage bottles)
I also wear a small mirror next to the primary computer to be able to see what’s going on behind me with valves, fins, entanglements, my slow buddies, etc.

This configuration grows nicely from backmount to sidemount, to multiple stages and deco bottles (just add SPGs and program primary computer for multiple gasses).