I'm a fan of simple, robust solutions and CO2 seems simpler to install, more reliable and more versatile. I have aired up 6 trucks on one tank from 15 to 35 psi running a mix of 31" and 32" tires and still had CO2 left for an impact wrench. CO2 does put out sufficient CFMs to run air tools where most vehicle mounted compressors do not without very large air tanks. I've also used my tank to tap kegs.

Running a CO2 tank compared to a compressor you have no moving parts to break, no electrics to short and very few connections to leak. I have an air hose that reaches all 4 tires on my truck without taking the tank out of the back and will reach most of the tires on a truck parked to either side of me or behind me.

The only down side is filling the tank. I have to drive 30 miles to the closest filling point, but usually do that on the way to the trail if I need it. And then it's only a couple times a year if I am selfish with my gas. It's around $1/lb of C02. So if you do go the $100 DIY C02 setup it will be many years before you spent enough on CO2 to match what a comparable compressor/air tank setup will cost you.