Office 365 devices

Hi,

Just want to check that where Office 365 says you can install Office applications on 5 PCs or Mac's, 5 tablets AND 5 phones, that means that each user could install Office applications on 15 different devices?

It's not meant to be 5 tablets OR 5 phones it is?

Is there is a license key, or do you just login with Office 365 account and that registers that device? Office 365 packages seem so much better than purchasing a license outright - late to the party I know. 

Thanks