I had no problem replacing my out-of-warranty SP4. Rep was courteous and professional. Replacement arrived in less than a week and was exact model in perfect condition. The bios did have to be updated but that occurred automatically on the first windows update.
I used Acronis true image to create a USB3 backup on my old SP4. The re-installed required I plug in a USB3 DVD (to boot Acronis) and then insert a USB3 flash with the Acronis backup.
Not sure if the built in windows 10 backup would have been easier to use but I have never looked into it. Maybe someone here has used that tool and can review how it works.