This seems like a good idea initially, but I think you'll find it's incomplete.

Here's the problem: for the employee, sticking their neck out and telling the truth is a potentially career-limiting move.

So they will never tell you the full open truth.

From experience, the best format is to use an impartial intermediary the employees do not report to, and whose stake is not in management's way of doing things.

Then employees can open up.

Why do you think Suggestion Boxes are anonymous?