It can have full functionality, it's just that it's currently only being sold on a Number Sharing eSIM service. You don't need to have your main mobile phone in the same room, or even turned on, in order to use this as an Android mobile phone.
Still, the sticking point appears to be price. That's the common view on other tech site threads.
This was the topic of a Reg discussion the other week - technically it's possible for UK networks to issue multiple SIMs for the same number (and a Reg reader confirmed a German network does just that - commonly used for a mobile and a car phone). Such a service would open up a whole menagerie of range of cheap and cheerful phones for use as secondary 'pub handsets'.