One big problem is the willingness to be honest. If you feel very unhappy and say so, even if it's anonymised there are probably means of finding out who it mig

One big problem is the willingness to be honest. If you feel very unhappy and say so, even if it's anonymised there are probably means of finding out who it might be (or the boss might even assume) and maybe even based on that fear an employee won't be honest. I think the idea of actually checking for this kind of thing is great, I don't just want to attack this, but I think it certainly requires a culture which is genuinely open to this kind of criticism, and in my experience that's incredibly rare.