Can be hacked to do more useful things
There are instructions out there on the internets on how to turn these into more useful gadgets than just ordering another roll of toilet paper (GIUF = Google is Ur Friend). Something like not registering them with Amazon, instead getting them to hit a server on your internal network.
Are these just launching in the UK now? They've been available in the US for some time, maybe a year. I do not think they automatically order things, they push them into a queue of some sort on the site, and you have an opportunity to kill the order before it goes through.
I do think the people that use these will be in for a general fleecing, as Amazon will start ratcheting up prices once it determines that you're a captured customer that doesn't shop around or price compare. Like boiling a frog.
And Amazon surely is selling the button as advertising space - I bet each of the brands listed have paid a nice sum to get their logo placed on a button. So this is a nice scheme by Amazon to separate fools/tools from their money.