Hi Mape,
It works the same as free version, but you get Guardian feature (password analysis and notifications when we get leak data with your logins in it). As for device count, not sure about unlimited, but if you use it on all your devices, you will prolly be fine. If you share it on some warez forums or give it to everyone you know, it will get banned tho. You don't need to enter it on mobile phones, only PCs and Macs as mobiles don't have the paid features. As for license itself, you can use it by entering license's activation key or by logging in with account you have the license on.
How well does it work? Well, I might be biased as I develop the Windows client, but I have it on all my devices, so fine I guess :-)
Dan