On paper, this socket cover (and its smaller single socket equivalent) look great - they're a pretty unique product that you can't get anywhere else and stop fingers turning off switches, rather than getting into them which is just as important. Unfortunately though, the truth isn't quite so rosy.
The problem seems to stem from the fact that there's no actual locking mechanism to hold the cover onto the socket; it has two raised edges on the inside top and inside bottom that hook over the socket, but nothing to actually hold it on. That means that while the actual flap section locks tightly and can't be opened unless you press both buttons in from the side (which is good), it only takes a tiny tug from the top or push from the side to dislodge the whole cover. There's another possibility as well, which is exactly what happened in my case: because hooking the inner edges onto the socket requires you to actually open/bend the cover slightly, the rigid nature of the plastic makes the whole thing try to return to its normal shape, making the entire casing pop off of its own accord after a while. It's like magic! Only the kind of magic that totally defeats the object of what the thing's meant to do.
It's a shame, because this is exactly what people like me with mischievous-fingered toddlers need. Unfortunately, my wife's original solution - gaffer taping a small ice-cream tub to the wall over the plug socket - works infinitely better than this.