>Most IoT devices are not designed to be used for extended periods without internet access and a continuous stream of updates.
But you could design one with a manual fallback option. Doesn't seem foundational to me. Nothing about an IoT design prevents one from doing that.
>The latter means that unlike traditional home hardware, once you install "smart" devices you're at the mercy of the business plans of the vendor. So even if you get something set up that works acceptably, it will last 5 years tops (see Nest) before the vendor's priorities change.
Yes, that is the downside of dealing with any service oriented business, in any domain. But again, you can have a manual fallback option (as I think most devices do FWICT)
>Finally to address the "extra security" comment. Security from what?
I suppose it depends on what you consider security. For an intruder alert system, you'd need something that can transmit a notification to someone. An IoT device seems like a good option, but I guess you could also use a device that can send a text over a cellular network.
I personally have no use for anything IoT, but I think its premature to go completely in the other direction and say that IoT is completely useless. What we're seeing with so called "disruptive" technologies is that things get worse (or sometimes a lot worse), before they get better.