There are a lot of reasons why it could a bad or just not a worthwhile idea for an individual, but some conspiracy theories on here are getting a bit silly.
The concerns about smart meters and health are the exact same ones as mobile phones of all kinds and wi-fi - that the radio frequency radiation that they give off is an issue. The levels are too low to cause an issue to human health.
Unlike most "smart devices", smart meters don’t connect to the internet and most don't connect to home Wi-Fi network, but to the same networks as 2g mobile data. Smart meters don't contain people's personal details, they're not linked to bank accounts. The main concerns about hacking comes from when there are other smart devices in the house connected to it (like smartphones, not required) and from malicious coders in tech companies using them to attack the grid. Malicious coding can happen with any smart device - when step 1 of hacking is 'get a job at the development company', as it is in that nickhubb article, might want to see the risk in perspective. It's a risk, but out of all the smart devices, smart meters are probably the lowest risk at this point. Some want to avoid them entirely, I can see the reasoning there, but a smart phone is far more of a security risk than a smart meter. They can be used to track when you're home or not and their security isn't really that much better most of the time.
In the multiple reports about the 'off switch', it's stated that the current gen 1 and gen 2 ones out there don't have this feature and it would require a legislation change for one to be put into the next generation - which is what is happening, SSE wants the ability and others are calling into question. If the signal drops out, the information is still stored and just passes along when the signal comes back - many of them aren't tracking at all times of day anyways and when it doesn't work, they turn into standard meters.
Yes, some companies have done shitty things around it. Some utilities companies have done a lot of shitty things when persuading people to switch or put them on terrible tariffs and some companies already have tariffs that are different depending on time of day. Whether the device could be useful to someone - like if their current meter is hard for them to use - doesn't really depend on whether some utilities companies are ethical. It depends on their personal situation and risk tolerance.
When you change anytihng it often goes wrong so why take the risk? - seriously? Yes, all changes have risks, but are we really basing our choices on this kind of fear that change so often goes wrong so 'why take the risk'? That seems weird to me.