For few years Ive used a free versiond of toggle. It was great but missing some features in free version. Paid was overpriced for me because I dont use time tracking app everyday so spending money each month was irrational for me.
Thanks God Ive found Tmetric!
+ one time fee for great tool for 25 users
+ great Chrome plugin and desktop app
+ I can select each entry as invoiced (billed) and see final report (with time roundig feature) but without obligatory invoice (thanks to that I can issue invoice outside Tmetric and mark time entries as billed in app).
+ many different reports that are saved to PDF (to sent for the customer)
+ add/edit/delete new work type for each project (it will help you to build structure of the project, not just flat "customer:Tesla-project:ModelX-task:Building SEO strategy" but "customer:Tesla-project:ModelX-worktype:SEO-task:Building strategy"
+ billable amount can be set at the customer/project/worktype/user level so it is very elastic (like Adam costs usually 200/h but in this project 300/h, and for that customer 400/h)

Few cons:
- Chrome plugin sometimes loggs me off (2-3 per month) - have no idea why
- invoice template builder would help to issue invoices that are correct form local law point of view (modifying header, items table and footer of invoice ).
- translation/internationalization for reports (that are sent to customer) would be a great feature

Must have if you are a freelancer or self employed who offer services, or if you are Project Manager who want to track time spent on projects by your teammates.