I’ll try to explain how it works. And I don’t mean how you use it. But how it technically/basically works.
The explanation is actually very simple
It simulates exactly what you would have done if you accepted your gifts through Facebook. There is no magic at all. Just plain simulation. Some times it’s eyes are not as good as yours and then it can be a bit slower. But some times it’s also quicker to decide what to do than you.
It fails…
…when you would have failed. So if it isn’t able to reject a gift, then you would probably not be able to reject it manually either. If it doesn’t collect a gift then you wouldn’t be able to do it either manually through Facebook.