We use LightStep to diagnose problems with our product, and it has been invaluable. It's great to be able to visualize an issue we're having without needing to rely on someone else's experience. It's also great to have a tool like this available to everyone. So far I haven't found anything I dislike about LightStep.
The UI could be improved, but there isn't much you can do in a web browser. Be sure to give them a try! We are solving complex problems with high availability requirements. This includes things like detecting when a system is down or experiencing a major failure, monitoring for potential issues, and visualizing where our systems break down.