I think a notice like this is a good idea. I've seen "security by obscurity" fail too many times. The size some groups.io groups is an opportunity for a clever phishing exploit. However, Bruce raises

#suggestion

After all the discussion on succession in the GMF, I suggest adding something like the new sentence in italics below: "It is a good idea to have at least one additional owner for your group as backup

The new help center looks good. As helpful as a help center should be. Clear and straightforward. Well organized. Notes: Liked the glossary tool tips. "Settings for Groups.io features" section: "Files

I'll second "adopt a style guide and stick to it." I also prefer the IBM guide, but following the guide consistently is much more important than the guide chosen. As much as you can, embody the style