The piece that really makes the kit special is the TTL support. Currently the only option is the Air Remote TTL-C for Canon but I understand that a Nikon version is coming. Both the flash head and the remote have USB ports so the firmware is updateable over time. The unit has three groups via buttons on the front but I've heard rumours that future firmware will support more groups.
The energy buttons allow you to control Flash Exposure Compensation in TTL mode, and basic output power control when not in TTL mode. Power control can be managed independently across Groups A, B and C. There are multiple channels available for radio communication with a range of over 100m in TTL mode. There is no documented limit to the number of heads per group. Canon's unit says a maximum of 15 600 EX-RTs can be controlled from their offering.
This is sort of amusing since you would need nearly ten 600 EX-RT units to match the max output of a single B1 Air.
The Model button turns the LED modelling lamp on and off and the Head button allows you to control which head you are working with if needs be.
The remote feels comprehensive not like it will fly apart in a strong wind. There's a sense of "pro" gear therein. The display is nice and bright and easy to read. I was also very pleased to discover that you can also make all your TTL group and FE comp settings from within the camera and they pass properly to the Remote Air TTL-C and then onto the head. Yes, I know this shouldn't be a surprise, but let's say other TTL radio options (like oh say PocketWizard) have been far below expectation. Some folks believe that the Remote Air TTL-C is overpriced. It certainly carries the Profoto premium ticket price, but take a look at the cost of Canon's own ST-E3-RT, a good device but more of a pain than the Profoto and like the Profoto it is a proprietary and closed system.
I also very much appreciated that I could set the flash(es) to either 2nd curtain sync or High-speed sync right from the Air TTL-C. Older reviews griped about the lack of HSS but I suppose the one I got had the newer firmware that added HSS support. So in that vane, the unit is fully firmware upgradeable via USB.
Moving on to the B1 head itself, again you feel the quality when you pick it up. Mounts are solid and lock up properly. The battery clips in properly and securely. The handgrip makes handling the head very easy. The head comes with a protective cap that when removed reveals the diffuser cover over the flash tube. This is the first strobe head I have every used with a basic integrated reflector and diffuser. It feels more robust to me than an exposed tube and modelling lamp.
Profoto uses a rubber ring with a clamp lock for their light shaping tools. Profoto tools are a lot more expensive than competitors. One thing that makes them different is that the external reflectors come in what Profoto calls zoom capable. This simply means that you slide the reflector mount to the degree coverage marker you desire on the barrel of the head. This could mean you need to purchase fewer reflectors in the long run. Profoto also uses their own mount on a speedring for soft boxes. It looks (on the web) like everyone else's speedring, with the exception that you have more control over how deeply into the soft box the nose of the head goes.
Many photographers don't start with Profoto gear and so may have an investment in other vendors light modifiers. I was not able to find an adapter to mount Bowens reflectors or speed rings on the Profoto. Elinchrom makes a Profoto mount for their collapsible soft boxes, and also make a mount converter to accept Elinchrom reflectors etc on the front while mounting to the Profoto head. I bought two of the Elinchrom to Profoto converters and they work just fine. I already have a mount converter from Bowens to Elinchrom so I will try that on top of Elinchrom's converter. It's not quite so elegant as a Profoto Beauty Disk or Magnum reflector but it costs considerably less than having to buy new Profoto light shapers. It works. It's not elegant and does change the angle of coverage slightly but it will do until I can justify Profoto branded light shapers
There are also numerous off shore light modifiers available with mounts to fit Profoto. In checking a variety of sources, reviews are uniformly poor citing low quality, poor fit, no fit, unreliable locking and other problems. The photographer who elects to go Profoto is best advised to sell off older kit if possible and replace it with the best he or she can afford. I did purchase the Fotodiox Profoto adapter for Bowens speedrings. It looks and is sized identically to the Bowens brand, and works just fine. I was also pleased to discover that the same adapter can be used with my Lastolite Hot style softboxes for shoe mount flash. Lastolite makes their own adapter but delivery was going to be a while and the price is ridiculously high.
Conclusion
The real question is "is this thing worth the price premium?"
When I first bought my Bowens, I did so because their light shapers were myriad, reasonably priced and their heads well built. I quickly became frustrated by their poor remote control option which is infrared line of sight requiring a blood sacrifice with every use and that I had to pay a lot more to get radio remote. Now of course, the PW cards are gone and Bowens offers their own proprietary radio control in most kits. Still no remote power setting or similar useful features. Because of this, and the absolute pain in the arse that setting up Bowens softboxes turned out to be, I went with Elinchrom BRX heads. Very light and a wonderful radio control system. But they don't handle abuse well and I am not nuts about the mounting system. Still they became my go to heads. And then I needed battery power. So I bought a set of Elinchrom Ranger Quadras, partly because my flash mentor, the inestimable Joe McNally recommended them as lightweight, reliable and lots of pop for the dollar. They work great, but you need to run cables from the power pack to the heads, and you need adapters to use regular Elinchrom light shapers. Still, a great system, except for that wire issue.
None of these solutions brought TTL. I still use a light meter. Many folks don't because in truth you can get to decent in exposure in three or four test shots, but I like the idea of the light meter, except when the subject is moving in relation to the lights. TTL, for me at least, has always been a good place to start, usually requiring a bit of flash exposure compensation but never really far off. Hence the simple love affair with the Canon 600 EX-RT setup. Light, transportable, TTL, lots of groups and independent control from the top of the camera.
Take the power of the Bowens heads, add the TTL capability of the Canon flash system, add the flexibility to use my existing Elinchrom and Bowens light shapers. Eliminate cables completely. Give me serious range. Add second curtain sync and HSS to studio power strobes. And control the whole thing from a robust legible controller on the top of the camera. That's the Profoto B1 Air system.