Very good question, but difficult to answer.
The only thing I can answer with certainty: Local save and restore via a PC works much better in any case.
For a while I frequently switched Internet boxes back and forth for testing purposes (IBS, IB2, IB3).
I estimate the result with the local save/restore to be around 95-100%.
What is missing always depends on the box and release, i.e. a subsequent check after the restore always makes sense.
There is certainly still room for improvement on Swisscom’s part, but you will probably never be able to achieve 100%, especially when changing models, as the settings sometimes differ.
Hobby-Nerd ohne wirtschaftliche Abhängigkeiten zur Swisscom