At the moment, you can only restore server A from backups made from server B.
Would be great to have an option to restore from any backup. I would use this for effectively branching and merging my work.
Server A - running in production. Make backup A1
Server B - spin this up to test some work. Build from backup A1.
when I have done my work
Server B - save backup - B1
Server A - poweroff and restore from backup B1.
this would quickly let me set my work live, without needing to re-do all my DNS settings to switch my domains over to Server B.