thanks 
just to note, i was only nitpicking, because it works awesome. I think the only issues might be in terms of "usuability", meaning people who never used either btrfs or snapper and are trying the first time.
but really, congrats dalto , sorry for nitpicking ! as you can see in my introductory : Greetings from new vm user , i mentioned that I preferred snapper to timeshift.
so ...a week later you appear with the solution I am very impressed ! if you wanted to impress, you did it !