Scubaroo once bubbled...
I run a backup with my Vytec, but my fiancee doesn't with her Cobra - I trust the air integration feature of my Vytec less, because it requires explicit calibration prior to the dive, whereas the Cobra automatically displays contents once turned on/submerged. Also, the Vytec transmitter/backup SPG combination still means a single HP hose - you would be looking at having two HP hoses on your reg. I would be more inclined to put the spare SPGs into your save-a-dive kit, along with the necessary tools to remove the Cobra console, and install the SPG, which should be nothing more than a pair of wrenches, or a single wrench if you leave the SPG on a spare HP hose, so you don't have to deal with the fiddly little spool inside the HP hose end during boat/roadside changeouts. At most, you cut one dive short, and you have less hose complexity on every dive.
Just a thought!