I am probably an exception, but when I go and fill my tanks I am using doing close to 750 cf or more.
I don't think that's too far off... I just filled 560CF from last weekend's outing, and that's just my tanks. Took about 3 hours, including taking care of the oil / filter change I was due for. I worked on other projects at the same time; no big deal. Pretty much par for the course.
With this compressor, at 3-4 hours per 80CF, filling tanks would quickly become an exercise in time management. Every 4 hours I'd need to go swap out a cylinder. Sure, it's a benefit that it can be left unattended. But to fill my 6 tanks... that's two days of switching tanks in the morning, immediately after work, and before bed. Miss one of those, and it just took three days...
Price is probably another serious factor - There are several new compressors available for just a little bit more, all in the 3-5CFM range. A new Coltri MCH-6 is $3750. Jim Sheldon will sell you a Bristol for about $3500. You can get a new Nardi, Maxair or Airetex for $3,000. I frequently see used Rix and Bauer compressors available for around $2400, and both of those are rock solid, proven designs.
Noise, the size and weight, and 110V power are all nice benefits, to a degree. My traditional compressor isn't all that loud. It's in my garage, and I can't really hear it once I get past the other side of the garage door. If I needed it to be portable, my buddy and I can move it no problem. Adding the 220V outlet was all of about $300, and 220V power isn't exactly difficult to find when out and about.
I definitely see it's application for airguns, when just one cylinder needs to be filled, and an overnight wait is no big deal. But if an airgunner were in the position of needing 6 cylinders over the course of a weekend, they'd be in the market for a larger compressor as well...