To use a back up SPG or not?

I have just received my new Mares Icon HD with AI and am considering keeping my SPG in case my wrist computer fails. Am I being over cautious or do most people use a wrist computer and a SPG? I will keep my SPG as a backup at least for the first few dives to make sure I know how it is functioning but once all clear do I keep or or put it to the side?

To me, having a backup SPG kind of defeats the purpose of going to an AI.

However, after having an AI computer, I've learned that I prefer the simplicity and reliability of an analog SPG.

For basic recreational diving, I don't personally see the need for having a SPG back up to an AI if you chose to use an AI. If something happens to it, then you end the dive and make a normal ascent. Because you will already be monitoring it on a regular basis and have a pretty good idea where you stand in regard to remaining gas, right? Keeping a SPG as a spare in your dive kit isn't a bad idea on a trip so you don't lose dives trying to get your AI fixed though.

YMMV

My answer is that it depends on your diving. 30 to 40 ft for 45 to 60 min would make me more comfortable relying on the link.

When I got my Luna I dove it for three months with an spg clipped off and needed it pretty often in the lakes I was diving. When I switched to ocean diving I went tens of dives dives without a loss of link and finally gave up the SPG.

I dive with the understanding that if I loose my link Or have serious link issues I call the dive.

If it doesn't bother you or get in your way why not keep it there?
If something happens to your transmitter at least you still have a working SPG.

My personal preference is to rely on an analog SPG. I've seen a lot of issues where the AI doesn't sync up properly when you're changing tanks. Requires a bit of troubleshooting when it occurs and it's usually sorted in the end. Personally I just don't get the hype of seeing my exact PSI when I can eyeball it to every 50th PSI on my brass SPG.

My best advice to you is to consider what type of diving you'll be doing. If you're doing deep dives where your plan calls for Deep Stops and Safety stops, you might want to have a backup SPG. Should my computer fail near the end of the dive I would want to ascend and do a short safety stop with my buddy, if I had the air. This is where an analog SPG would come in handy for you.

On the other hand if you're doing shallow dives or planning on skipping any safety stops should a computer fail then a backup SPG probably isn't necessary for your dive plan.

Overall I trust most AI computers to be reliable enough to give you an accurate reading.

My wireless AI seems to be completely reliable but the SPG is out of the way so I leave on my rig.

I needed it once (long story) and was glad to have it at that time.

My computer isn't AI, so for me no choice. If I had an AI I'd still use the SPG as well. Another question like--do you still use tables when you have a computer? Can't hurt.

I am AOW diver but very rarely down past 100'. I will keep it for a while I was just trying to get some opinions from others.

After a safety stop I figured I would bleed my tank down to 500psi and perform a weight check. Well it turned out the stupid computer didn't react fast at all and the next thing I knew it was reading 750psi and I received a harder pull of air. Figuring I had just passed my weight check I casually surfaced with probably less than 100psi in the tank. Haven't dove since without a pressure gauge clipped off to my hip on a 24". Although now I also got away from the AI computer completely and use a Tech 2G so I have a second timer to time deep stops.

RDRINK25:

I am AOW diver but very rarely down past 100'. I will keep it for a while I was just trying to get some opinions from others.

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Just to clarify, it seems you're kinda referring to my post about diving deep. I consider any dive below 60ft to be deep. I usually plan a 1min Deep Stop @ 40ft whenever I get around the 70ft mark, even though my computer doesn't have it programed until 80ft.
As for when I would do a safety stop even with a dodgy computer, it would depend on the situation and dive plan.

I think it's a good idea to try it out, just to see if it bothers you having a backup clipped off somewhere.

I have an AI computer but it doesn't automatically sync. I have to do that manually at the beginning of every dive. Yes I've forgotten a couple times (gotten interrupted by students during my pre-dive routine), yes the transmitter battery started to die a couple times in 5 yrs (boy did I get some wiggy PSI readings that day), so I'm glad to have a small spg tucked out of the way for back up. I also dive with a backup non-AI computer when I'm doing alot of diving. Don't want to get sidelined by a malfunctioning piece of electronics.