I just got my havak PH1 last week and asked myself this same question! I also read that review where the ATC comes in the middle of the pack. I also heard the 419 Hellfire directs blast backwards, but only a few reviewers stated this.
I went ahead and purchased the Hellfire (received it in 2 days so I got it before my rifle was in). I am really happy with the Hellfire-- that said, I did not shoot the rifle with the ATC brake. Install was probably the easiest you will ever find for a self tuning brake-- it is quite genius the way 419 designed it! I found recoil reduction and muzzle jump to be quite good. I felt less recoil shooting this on my havak than a different brake on my buddies 12 lb rifle (same caliber). I also did not notice any muzzle blast coming back at me.
Just buy the Hellfire-- it is worth the $$... if you have it