Realize that an interview is not a standardized test. It's a date. Most candidates make the mistake of thinking that it's a test, which leads to a lot of agony.
When you dig deeper, you'll likely realize that an interview outcome is just a fuzzy function of multiple interviewer's subjective preferences, very much like a date. And when you get reject a date (or someone rejects you), it's often not possible to put a finger on a crisp reason, more than "it didn't feel right".
What is in your hands, is just preparation. Once you have done comprehensive preparation, then you have to leave it to luck. Hope that you get seasoned interviewers who can evaluate you objectively in that hour.
As an employer, no I would never sign this and share as there are just way too many liabilities attached even if we had done all the right things.
However, I have had people that interviewed with me and didn't get the job send me an email and thank me for the opportunity to interview and ask me what I feel they could do to improve, work on etc. I won't reply to all of these, but if someone asks a specific question I will more likely reply. For example, I had one guy that wrote something to the affect the he knew he flubbed part of our algorithm questions but he was really interested in that work and was curious what I thought he could work on to better his skills.
I replied to him and told him things he could work on, and really very little of it had to do with what he flubbed. In his case, I suggested he work on his communication skills and reminding him that an interview is a sales process, he is there to sell himself to the interviewer. I also explained that his algorithm flub wasn't a big deal as it is more about ability to learn than always knowing the right answer. In this way, I gave him valid, constructive feedback without putting us at great risk. Although I know some employers wouldn't allow a hiring manager or team member to respond, but finding that person on LinkedIn etc outside of his work role and learning how you can improve might work.
Also, find a couple of friends and do a post mortem on your interview to the best of your recollection and see if they can give you any hints or ideas.
Since interviewing is very subjective, a company might not even be able to give you a clear reason why you were rejected. You may have been interviewed by six people, each of whom gave you a 9 out of 10 rating. You thought the interview went very well, and so did they. But then those people interviewed someone else, whom five interviewers gave a 9 out of 10 rating but one gave a 10 out of 10 rating. So they chose the second person instead of you. But there may not have been a clearly expressible reason why - just one interviewer's gut instinct.
Also, they may have rejected you for a stupid reason, like "the CEO didn't like your blue hair and nose piercing", which they may not feel comfortable sharing with you even though it's perfectly legal (under U.S. law, these are not legally protected attributes).
If you sign and they advise you that you were rejected for an illegal reason, they can be charged for that crime, and if they are guilty, you can sue for $$.
If you sign and they give a rational and reasonable reason, like you only received 15 points on their rating system, and they chose only prospective employees who received 25+ points on that rating system, then you agreed to not sue if they revealed and you can not.
That said, there are many nuances in this, however, any company would be a fool to codify illegal acts - if they have their own lawyer, so you might not get anywhere.
I would say, sign and get the details, and if they can not be changed by extra study, get going and improve your score.
A lot of people never get criticisms on which to base self improvement.
Realize that an interview is not a standardized test. It's a date. Most candidates make the mistake of thinking that it's a test, which leads to a lot of agony.
When you dig deeper, you'll likely realize that an interview outcome is just a fuzzy function of multiple interviewer's subjective preferences, very much like a date. And when you get reject a date (or someone rejects you), it's often not possible to put a finger on a crisp reason, more than "it didn't feel right".
What is in your hands, is just preparation. Once you have done comprehensive preparation, then you have to leave it to luck. Hope that you get seasoned interviewers who can evaluate you objectively in that hour.
[about me: http://InterviewKickstart.com]