The viar makes .64 cfm at 90 psi to the fortress's .7 at 90 psi and the max psi is 15 psi higher thank the viar, so I'm not sure it makes less air.
The Op's question was for a compressor to fill tires on the road (mobile). The Vair mentioned makes 1.25 CFM at 30 psi or 1.15 CFM at 40 (typical tire pressure in a RAM 1500) . The Fortress isnt going to do much more then the rated 0.7 even after you quickly deplete its little 1 gallon tank.
I have the Senco PC1010N that harbor freight knocked off (re-branded) into your compressor. Love the little thing. Super light, quiet is an understatement. Its great for little nailers, filling my timber grove air bags, maybe a couple shots from a framing nailer, topping off a tire once and a while That is about it. Stinks for air tools, blower tip..... I can pull out the MV-50 in the same span of time, don't need an inverter and air up nearly 3 tires in the time that little guy can do 1.
Big trailer tires that require more pressure and could benefit from a larger duty cycle. Now that might be the ticket for the Fortress. Or even better for the same money consider a Porter cable pancake for twice the volume (If you could stand the horrid volume).
Just my 2 cents. What works for you might not be what works for me. I do appreciate that the forum allows for all these ideas to be submitted and debated. Would love to hear about your inverter setup. Been on my want to do list for quite some time. Even have a large Tripplite inverter (transformer based) sitting on the shelf for a couple years now waiting for the time to make it happen