Apparently MU has missed the posting from Sampler, below, that this app is FREE. Paid registration is optional, and enables certain unspecified fancy features (the only one mentioned is "HTML Export", whatever that is).
From the app's splash screen
"SourceGear DiffMerge is an award-winning file diff and merge tool that has been helping professional developers and hobbyists since 2007. SourceGear DiffMerge is licensed for use free of charge. However, by registering DiffMerge you will help fund new product development, maintenance, and support. As a way of thanking our registered users and encouraging additional registrations, we have added some new features in 4.2..."