In order to operate the mechanism of control, something force has to be expended. That would never make a child. Therefore, before top.
Installation is also very easy on the hand. Open the window or the door, lift the cover under the window handle and turn it 90 degrees, loosen the screws underneath, insert the fuse between handle and door. Screwing, finished. With the suitable screwdriver that is less than 5 minutes effort.
The window or the door, making it really well secured and you as parents just a better feeling when you know that nothing can happen!
Price / performance is also really great!