Do they work completely locally or just without the Roomba app? I mean, if you prevent the i-series from phoning home, does it still work? I guess I could test this pretty easily, but frankly will be pleasantly surprised/impressed if Roomba let their robot run “off-grid” for very long.
In my experience, without wifi, roombas are loosing their schedules after some time. I don't remember exactly, after couple of weeks maybe. They just stop working according to schedule or star they work on unusual hours.
Update: pleasantly surprised: https://iroboroomba.com/how-to-use-roomba-without-wifi/