You should be monotoring your SPG often enough duiring the dive and be familiar enough with yout gas consumption rate at a givne depth to be abel to anticipate the SPG reading when you look at it each time. It is often the discrepency between what you read and what you expect that alerts you to a problem either with the SPG or with something else occurring during the dive.
If you do not think about and anticipate the SPG reading then if you dive long enough you are eventually going to have a nasty susprise during a dive.
For example, I once had an Uwatec quick disconnect come undone just enough to trap the gas in the HP hose. This was immediately noticed at 100' on the next spg check as the SPG reading had not changed as much as expected and another check a minute later confirmed the reading was not changing. Since I had been monitoring the SPG frequently and could extrapolate from the last valid reading (the one prior to the less than expected reading), I knew I still had enough gas to do a normal ascent, safey stop etc. Had I just been checking the readings without thinking about them and anticipating the expected number, I could have blissfully continued noting the still 3/4 full tank reading and ran the tank dry while congratualating myself on my excellent SAC rate.
Specifically with the Wisdom, I experienced a failure in the dive computer, but the SPG continued to provide pressure information. A second Wisdom failure resulted in the SPG reading 245 psi when not connected to anything after the dive. Neither situation left me with a lack of tank pressure information or wildly inaccurate tank pressure information.
The most serious SPG failure I have had was a failure with an Aqualung Digital SPG (an attempt to get the predictive qualtities of air integration with the advantage of separate deco and spg functions) that completely shut off at depth when the battery cold soaked in the 35 degree water. Again, I was monitoring enough to know what to expect so I basically still knew what I had with reasonabel accuracy and knew I could safey do a normal ascent.
So in effect, based on my experience, an air integreated computer is potentially less relaible than a standard mechanical SPG (I have never had one fail in 23 years of diving) due to the greater reliability of the much simpler and non battery dependent design traits. But on the other hand, if you do your part, an SPG failure is not a crisis but rather a minor event that is readily handled by a routine abort of the dive.
For a recreational diver who spends most of his or her time at shallwo depths where the dive is gas limited rather than deco limited, and where a direct ascent is always possible, an air integrated computer may make sense as the air time remaining function may be useful - especially for the occassional or less experienced diver doing multilevel dives (having that function is a good way for you to rapidly get up to speed on the connection betwene psi and time remaining at various depths.)
On the other hand I have found that air integration offers no real advantage for a diver who is monoitoring and interpreting the SPG properly as you basically do the same predictive air time remaining computatons in your head once you acquire a little experience.
If your goals include techncial diving, an air integrated computer is not the way to go and a conventional SPG with bottom timer or 2 or 3 gas computer is a better choice.
My personal impressiona dn expereince with the Wisdom is that the later Wisdoms were much more reliable than the early ones and I am assuming, even though it is not being said, that the improvements in the Wisdom 2 also include changes to increase reliability and reduce potential for failure.
