The longer handles require less input to the kite. They allow the kite to be be controlled at greater angles to the wind.
Some may take issue with my answer to the second part of your question.
The bend angle, geometrically, makes no difference at all. Any difference in the bend angle can be compensated for by the length of the pig tails at each end of the handle. Think about it. If the handle was straight, you would want short pigtails on the top, and very long pigtails on the bottom. If the handle had a 90 degree bend in the middle, below the grip, you would want very long pigtails on the top and very short pigtails on the bottom.
The distance between the top and bottom pigtails is what controls the amount of input required to control the kite.
I had Mr. Hunt for geometry.
We fly with fairly long pigtails on both ends of the handle, allowing nearly infinite adjustment of the angle of the grip portion of the handle. In very high winds, we keep the grip as close as possible to a neutral position to ease strain on our wrists.