I think notifications after updates make more sense. You already know the software, and you are informed of some new feature that you may or may not care about. How else can a user be informed about a new feature else? Even if I do not care about the majority of features added, there is still occasionally one that I may want to use.

I often read such notes/product tours in software I already use/know, and in contrast I find it a bit stupid when they add some feature and they do not tell the users. It should not be obstructing, though. I would say the updating itself breaks the workflow more than a pop-up window or sth.