With a good router, it's not that hard to do. But even then it took me a long time to get around to setting up the separate network, and I don't think I've migrated all of my devices over to it still (some got moved, new ones go there, but there are some older devices still sitting on the original network). So, yeah, there's definitely extra effort, and it's not really fun like getting that new smart device integrated. I will say the stuff on that network works perfectly - I haven't noticed any side effects.

Oh I did allow them access to the pool ntp server so they can pick up the correct time, and some require temporary access to the internet while setting up (the linknlink RF device needed it to download the Home assistant version of their firmware, for example).