Unless there's some highly sensitive information that you want to disclose, I would not suggest making this anonymous. In general cases like this one, anonymity does not help. In case the feedbacks are true and you expect some action to be taken based on that feedback, you should be able to own up the comments mentioned in the feedback.

Also note, a feedback does not always mean negative criticism (which usually does not go well with the recipient) - it also involves shout-out to the good things also and encouragement to carry on the good deeds.