Knighthawk user here. I am also new to this BC coming from a Pro QD+. What I found out to be true with the back inflate is I have to sway a certain direction to get the bubble where it feels like I am not rolling to one side. Im not sure if you dove with a back inflate before, but it is entirely a foreign feeling from the jacket style squeez.
Also, I recently discovered on the Knighthawk that I have to dip my shoulder a certain way to get the dump valve to work. Same goes for the power inflater to release air. However, I have come to a conclusion that I stop using the power inflator to release air-it just doesn't cut it. I either have to be completely vertical or stop what I am doing and move the bubble to the low pressure hose...:no NOT MY FORTE.
Next, the Knighthawk, as stated above has a secure tank strap, a little adjustments here and there to get the right fit on your tank and you're set. Try it on, and feel the way the should straps touch the top of your shoulders. This is where I feel its uncomfortable. Remind yourself, this is on the surface, when you are underwater this changes.
At first, I felt it was indeniably the worst BC, now after some more dives I am starting to adjust how I dive and put weight where it needs to be. (trims, +/- in either weight pockets, etc..)
I hope this helped.