Overall, a functioning and useful extension despite some roughness. For example, to not tag certain subreddits, you need to move over both copies of the subreddit name. I have no idea why most (possibly all) subreddits are repeated, but I'm guessing that's the main cause of issues people have with the not tagging feature. Also, remember to save.
For all the complaining, there are very few subreddits that seem out of place. The only major subreddits I don't tag are conspiracy, drama, and pewdiepiesubmissions. I'm no fan of any of those three, but I found that users who were only tagged as one of those generally weren't worth tagging. That's just my personal preference, but there is an objective issue concerning the milder subs and subs that have changed from milder roots (TiA, imgoingtohellforthis, cringeanarchy). The default alphabetical tagging priority is fine for all the roughly equally vile subs, but I'm pretty sure most people would rather a user be identified as a whitenationalism poster than a prolife poster. It would be nice to have the subs where all users are despicable people in a tier above the less definitive subs. Of course, these gripes can all be fixed manually, and the developer seems committed to his own judgements being reflected in the default, which is obviously his right.
As for the actual experience, it's interesting. It's definitely helpful in controversial conversations, since good-faith inquiry is sometimes hard to distinguish from obnoxious trolling and/or shitty persuasion attempts. The tag certainly tends to aid your ability to guess which is going on. On the flip side, it's nice to have positive exchanges with (some) tagged users in more casual subreddits. I don't want to socialize with and potentially see good in a rapefugees poster, but it reaffirms shared humanity when I have a positive interaction with a conservative tagged user in a sports or food sub.
Oh, and five stars despite some technical and design flaws because it's serviceable and the only option I know of.