If any of it uses cloud services or requires internet access to function, then it's harmful. It will be gathering lots of personal data that will be sold. It will stop working if the company goes out of business or just decides to stop supporting your hardware or if they ban your account for whatever reason they want.

If it's all self hosted on your LAN, then it can be convenient, provided that whatever it controls can be manually operated if there is a problem. It's even better if you are using all open source hardware and software.

An absolute nightmare for security and privacy. Just say no.

I like mine. It has a lot of nice convenience features, and it feels good to have stuff happen automatically based on your presence. Scripting useful automations if a time-consuming hobby though, and if you're mostly just interested in doing voice control for lights it may not be worth it.

I'd recommend staying away from anything that connects directly to the wi-fi if possible. ZigBee lets you isolate the garbage hardware from the Internet so they can't be used as zombie devices in a botnet or worse, and have home assistant be the one point of contact.

It's a great and rewarding hobby! But having cloud connected devices on the same devices as your sensitive information is an issue.

Use a vLAN and IoT devices capable of local control. Use a self hosted hub like Home Assistant. Keep devices that collect sensitive information (like a camera) out of sensitive areas (like the bedroom). Then you should be reasonably secure.

The only smart objects I have are some light bulbs. I think, some processes are good to automate and put software in control of, and some things I want to have explicit control over (I.E. Door locks, Safe locks, AC settings, Heating). Technology can break in fantastical ways, but a lock should just freaking work.

I love the idea of having motorized blinds and windows that automatically open/close coordinated with thermometers to regulate house temperature.

As someone who has spent many years working on my smart home, I suggest, as do others, KEEP IT LOCAL.

It's convenient but it's less secure and less reliable. Imagine being locked out of your house because the Internet is down.