doffactory can you tell us how quick is a recovery from a backup?
Sorry, no, I can't. I've never used Seedvault to restore a backup. Theoretically, it should be pretty fast depending on how much data is being restored.
doffactory do all the settings migrate with the backup
Yes, but only for apps that were backed up and restored successfully.
The API that Seedvault uses is an old one that Google has depreciated. Without getting into too many details, just know that many app developers block backups using this API for security reasons. This means many apps won't be backed up at all.
People have had varying results with Seedvault. Some claim it worked perfectly, some say it didn't work at all. I have read that GrapheneOS developers are going to replace it at some point, but I have no idea when that will happen.
If you choose to migrate your profile and want it to be easy, maybe back up with Seedvault first, then be prepared to restore some data manually that Seedvault missed. Or just skip Seedvault and do it manually.