Badly organised installation campaigns with each company using different meters are rather farcical. I believe the aim is for the UK to get this sorted out but I don't know within what time frame - until then I would suggest they are to be avoided. Otherwise I think the main point is that billing will be accurate without needing manual readings at frequent intervals - to me that is worth having.
With the universal use of smart meters it should become possible to change suppliers instantly if the customer wants - mind you it should already be more or less possible but it is said that the Ombudsman dislikes such convenient flexibility and insists on one being trapped for at least two weeks with the old supplier, including on moving to a new home (which sounds believable, seeing as here we are speaking of the UK).
Yes, if one fails to pay then one should expect to be cut off - why not ? If an error occurs (unlikely I would expect/hope) then reconnection can be done remotely and instantly (compensation claim pending). As for savings using smart meters, my understanding is that the argument for that relies on equipping you far self-limitation of consumption, in effect a kind of rationing - this I find daft, everyone surely knows that abstention reduces cost.
The supposed health risks and the data thing sound too much like a reliance on conspiracy theories along with the instinctive secretive nature of some. If hacking really is a risk then that needs serious attention although simple vandalism would seem the only motive for hacking and therefore for most this would seem a somewhat unlikely risk (unless I am missing something).