It took me a lot of careful drilling to get these things working cos you do have to drill quite deep into your door or the magnetic system doesn't work but there are little extension parts if you do have thick doors. They are also quite tricky to use cos you have to get the magnet in just the right place or they won't open.... my mother in law doesn't even try anymore!
But all that said, they work brilliant! Our little one is no longer interested by what's in the cupboards cos she knows she can't get in. And unlike most other systems which have to open a little in order to work, these don't open even a tiny bit until the magnet is in the right place so there is no chance of a little curious finger getting caught.