Many of my customers are having problems with the license model for testers where a non-frequent tester (for example Acceptance tester) has to have at least a Visual Studio Test Professional to do their test even if they only run test in the test hub in TFS Web Access.
This changes next year!
In January Microsoft is including test execution capabilities in the test hub into the Basic level of VS Online, people who need to manage tests in the test hub can use an Advanced license and people who need the full Microsoft Test Manager set of capabilities can purchase Visual Studio Test Professional or above.
In the on-premises version of TFS, TFS 2015 Microsoft is including test execution rights, using the test hub into the TFS Client Access License (CAL). User who need more will need at least Visual Studio Test Professional or above.
Read more about licenses here: