Forgive the long post, I will share what I have come across and hopefully save some others some time. I was confused as well when I was researching them, the info out right now for the fords is not the greatest. They come in a couple different flavors for the psd, the 130/55 and the 130/75. Both are designed to replace the stock HPFP. The 130/55 is preset at 55 psi and the 130/75 is the adjustable model, adjustable from 45 to 75 psi. They are designed so that you unplug the outlet hose from your HPFP and the airdog 2 hose has a quick connect that will plug right in to the factory line that goes to the engine. The airdog 2 is supposed to have a more robust albeit quieter pump than the first generation airdogs along with the 75 model being adjustable. It is worth nothing too that I believe all airdogs come with a lifetime warranty to the original purchaser.
I was planning on doing an itp regulated return fuel system so upon doing reserach for that upgrade, I ran across advice from Dennis at ITP. I don't want to speak for him for fear of misquoting, but basically he recommends running the airdog as a helper pump to our factory HPFP and keeping it at about 10 psi because that is where it removes air the best. At higher pressures it becomes less efficient at removing air because the bubbles get small as the pressures increase and pass through the filters on the airdog.
What I ended up doing is getting the airdog2 130/75 setup and then got the duramax regulator assembly from pureflow (Toby and Ron are great to work with and helped me out with deciding what to do to make this work how I wanted). Basically this allows me to run the Airdog2 at 10 psi as a helper pump to the stock HPFP, then I have my fuel pressure at the regulator set at ~64 psi with the itp regulated return system like Dennis at ITP recommends.
The regular airdog is a 10 psi helper pump that plumbs in before your stock HPFP. Both systems come with everything including all fittings to do the install and are quality kits. Looking back I could have just gotten the airdog 100 or 150 but I always like trying the new stuff that's out there.
Also if my stock pump ever goes, I can swap out regulators in the airdog 2 and remove the stock pump and not have a problem. I am interested in hearing what others think of the airdog 2 as well.