This app is very useful and even if i have more complex ones, i think the best lies in the fact that's fast, easy to integrate and well coded.
The UI and UX are both great and the founder is active and listens a lot when there are constructive feedback.
Last, the terms are very very good and it's a no-brainer!
If you have a site that's being launched and need to quickly fix and collect feedbacks, go for it, it's a no brainer! (and this is only one of the various use cases it can cover)