Double ball catches are easy enough to install if you still have access to the inside of cabinet. If you are planning to use these catches on anything but the most rigid cabinetwork it is advisable to mount them horizontally at the bottom or top of the door. If mounted vertically, opposite the hinged side of the door, any small amount of racking will change the lateral relationship between the parts and prevent the catch functioning correctly or worse. Plan also to fit them before the backs go on.
Mounting these catches on an otherwise finished cabinet can be frustrating unless you are blessed with an extremely small assistant with a flashlight. Without help of this sort you will be obliged to rely on measurement. Even with the most painstaking measurements I have never been right the first time but a little fine tuning of the male component with a file is usually all it takes. The nature of these catches suits them to fine furniture rather than cabinet use as reliable functioning requires precise relationship between the parts to be achieved and preserved.