Security.txt (2017)
I understand and welcomed the initiative when it was first discussed. Meanwhile I've implemented it on a couple of domains and hat it running for all of 2018. Last month I removed it all again (the sites still have a responsible disclosure link but not at a standardized URI).It was a massive waste of time for me to engage with a group of "unknowns" -without prior relationship- who now had a channel to fast-track into my inbox (and got my attention).The volume of mails was anywhere from 5-20 emails per week which is a lot if you need to go through the points in every mail but you don't have any idea if the entity behind the poor-security-report is even skilled. So you start in good-faith that the report they gave you (e.g. you tell yourself that your own time analysing it is justified "they're probably competent", "they know what they're doing otherwise they'd have a different job", "maybe somebody will get lucky this time", or depending how many bad reports you already read you might be down to "even a blind chicken finds a kernel of corn every now and then")it seems I ended up having endless discussions with people who automated the whole thing: they crawl the web for /.well-known/security.txt URI and if the find it, automatically start-up metasploit or burp-suite and then send you the canned report while asking you to fix these "serious problems". 
Yet if you quiz any of these "researchers" deeper about individual items in their canned reports you get nothing but blank stares, incompetence and attempts to weasel out: "but burpsuite says that it is an error and you should correct it", ...Initially I went through every email patiently. I tried to engage these guys on why they strongly felt it were vulns or 0days (LOL). I knew what they reported was canned and they never questioned the context or the errors themselves. None of them were people that I would hire or trust to give me good advise. Advise wasn't always just bad. Often they have a whole consulting company sitting behind them who not only "fix your problems" but also migrate your whole stack to Drupal or Wordpress or some such nonsense.If I look at the other end of the spectrum (infosec-memes and "thought leaders" on twitter) I get people complaining that some customers just don't know how bad their security is and they even dare to ignore their reports or worse (question them on their authority in whether this is a bug or not). The whole thing is the deaf leading the blind here. I get what security.txt was trying to improve because there is/was a real issue for people to find a point of contact. But I do not think security.txt is in any way useful. And it's a total waste of time and money for small companies and bigger companies alike. (if you're bigger you get more attention = more reports but that doesn't improve quality - it only adds more work on your end because now you have N-people (instead of 1 or 2) discussing these constant "non-problems".