A locking window handle is mainly used for child safety, but with certain break-in methods it can also serve as security products for windows.
Especially for parents, locking window handles of this sort are a good idea because they can control which windows children can open. As the handles are available in a keyed-alike version, you only need one key to unlock all your window handles.
Some window handles, e.g. the FG 300, are designed in such a way that they can be used in any circumstances. The square spindle can be adjusted to fit any window. There is therefore no chance of buying the wrong thing. And they are very easy to fit.