I used this feature today to migrate from an older device to a newer one. It worked pretty seamless apart from a couple of issues:

1) I got some network errors when importing the old config. This then “hid” the progress bar.
2) The page never then reloaded. But a ctrl + r took me right into the login page.
3) my z2m had to have a new config applied against it before it would start. But that’s a 3rd party addon, so I can’t complain.
4) It didn’t change the IP.