Our feedback feature allows you to ask for a star rating (between 1-5) and collect a feedback message from the owner participant once a plan is completed.
You can enable feedback by opening a template, and clicking Template settings on the main template page. Then select Thanks page. You'll see a page like this:

Make sure Also ask for feedback is selected (it's on by default). Click Save changes when you're done.
When the owner participant completes the last task, the plan will be set to completed, and they'll be directed to a thanks page that also includes a feedback section:

The rating is available as a column on the plans list. It's a good idea to create a view that allows you to periodically review completed plans and their ratings.
This is a view with the rating column showing:
