I am not familiar with Harmony, but Harmony is a library whereas Typemock is a mocking tool; Harmony requires to \"patch\" manually in order to get things to work (modify methods behavior) and from a quick review of the documentation it has some other restrictions (i.e adding fields to classes or correct me if I\'m wrong).
It looks like a great project to me, but it pretty different than what Isolator for .NET offers (SmartRunner, mocking friendly API, Suggest, Coverage... and well, the price ).