The HL hook is a strong yet simple hook to use, inside the hook there is a three ball-bearing system that grips the hanger as soon as you let go of the button. Also due to this ball-bearing mechanism the more weight you add to the hook, the tighter it grips.
The hook itself holds 20kgs on the steel hanger, this weight restriction is of course doubled when you are using two hooks per picture, check the hanger that you are using has the correct weight restriction also as some systems have a lesser rating on their hangers.
This hook is robust but small, extremely easy to use and can be adjusted by the millimeter.