The damage occurs when the boga is clamped down on the jaw... Watch someone using a boga, the fish immediately "freaks out" as jaw gets clamped, maybe pain or just fear... The fish typically will spin over and over, damage can occur without the fish even being lifted out of the water. Lifting the fish out insures damage.
as far as releasing kings, seems like it works, esp. since some have had success, might even try it with a #2 barbless hook attached to some wire.
I actually just think its common sense, not surprizing that some find hard realize though...