h2 is not a wiki BB-Code. "H" is. H2 and H=2 are not the same BB-Code.
For user tagging, you have pointed out that there is an inconsistency in behavior between tagging in the latest XenForo vs the latest VaultWiki. In VaultWiki, user tagging only works when the comment is initially posted. If you try to mention users in a later edit, as was done in that example, it will not work. This was originally done to avoid a situation where the same user kept receiving an alert for being mentioned every time the comment was edited, but it has resulted in the inconsistency you see. We will have to look for an alternative solution to that issue. I have Confirmed this as a bug with respect to that.
I have just mentioned you in a comment to make sure that user tagging was working at all.
Unfortunately, with that being a demo site, we are going to test things on it, and other users are going to test things on it. In a lot of cases, test content is not going to be attractive to a potential buyer. Some tests are going to look like garbage in order to see if the wiki can handle garbage without breaking down. But I'm not sure if there's a way to resolve that -- the point of a demo is to allow the potential buyer to try things out for themselves. The only thing I can think of to improve that in the comments, without actively removing other users' tests, is to bring back the ability to reverse the order of comments to newest-first (an option that has regressed).