Having working in management for years, both middle and upper, internal and external, as founder and in other companies: I have quite a strong stance against "confidentially".

Because the reality is that 80% of the typical workforce (maybe even more in the case of engineers) has a lot of comments about how things could be better and how their manager is doing it all wrong. And those comments tend to come out in an unnecessarily strong negative form if you provide an anonymous forum. But most companies don't need more people telling you what's wrong, they need people that take a responsibility in improving it and move things forward.