NOTE: this is the review of the extension, not of the TMetric service. The service is great, 5 stars hands down. This review is strictly about the usability of the browser extension for that service.

Not having to open a separate tab to run the timer is very convenient. But at the same time, I feel the extension lacks a few critical features to be convenient to use:
1. It doesn't show any kind of tracker in the browser UI. In fact it's not at all clear a timer is running except that the TMetric icon on the toolbar is colored (it's grey when inactive). Perhaps an overlay with minutes shown could do the trick.
2. It doesn't pull existing task titles from the database, so you need to enter task names every time manually, risking typos that will result in multiple tasks in reports where there should be just a single task.
3. And it insists on using the current browser tab title as the task name. It may be useful for some, but not for everyone; would be good to have an option to disable this.

A few quick links to the main site would be good, e.g. Reports and Manage.