I have both the Solo (actually have two) and the INH05 S version. I have read allot of the messages in this thread and had a careful look at the Air (but I do not own one). I agree that the Air is a smaller version of the Solo with battery replacement and if I had to replace my Solo, I would most likely do so with an Air as I have two Solo's anyway so if one went down I would buy the Air and have an Air and a Solo.
Saying that I really like the INH05. I think the INH05 is slightly more stealth than the Air due to the glass mouthpiece on the Air and the capsule for the INH05 which is under the cap.
Arizer is a great company though and I am sure that you can not go wrong with an Air as the Solo is a solid piece of equipment and I have no doubt the Air is too. Saying that if I had to choose, which I did, I chose the INH05 (I do have two Solo's though).
The INH05 battery life is a bit better than the Air. Battery replacement is easier in the Air than the INH05. The INH05 is USB charging. The INH05 has better temperature range both for lower and higher range but not that big of a difference that I would let this alone determine my decision. The heat up time of the INH05 S that I own is 25 seconds which is AWESOME. I am vaping in less than 30 seconds if I need to. Lower temp, less clouds, great taste. Higher temp, better clouds, great taste but slightly harsher due to the higher temp. You can use an additional mouthpiece or buy the aero capsules which allow you to set the amount of air intake with the vapour. Nice feature.
The two units are different and again, if I were to get another unit to replace a Solo it would be an Air.
If you do not have a portable vape, it is a toss up. The reason is that (as stated in an earlier post) they both rock.
For me the final deciding factor was stealth. I found that the glass mouthpiece at the top of the Air less stealth than the mouthpiece (capsule) on the IN05 (base or S).
I also have an Ascent that I use. I have had the Pinnacle Pro, Davinci, iTorch, MFLB and iolite as portables.