As I understand it because the hook eye is in an almost straight line with the hook point it gives a direct in-line hook hold that hooks up better than the offset hooking angle of a conventional hook, plus once hooked the fish finds it almost impossible to find any leverage to twist it out as long as line tension is maintained.
The cranked bit gives a wider gape between hook point and shank than a curved bent shank or an inturned hook point, further increasing the efficiency of hooking up.
It is also said to be more fish friendly for hook and release as, because the force on the hook hold acts in a straight line, there is no tendency for the hook to cut sideways or enlarge the hook hole.
They are said to be so efficient in comparison with standard hooks that I believe that the american air force (or marine flying corps, one or the other) has taken the step of putting them in the survival packs every pilot has in case of being shot down in the middle of nowhere.
I'd be interested in giving them an experimental try if anyone knows of a supplier in this country.