While looking in a specific commit, there is no "External Diff" (SourceTree 1.8.2.3 on Windows 7 - 10)
And also no "Open in Explorer" in this context menu.
It was ok in previous version.
But, it is still ok when looking changes in Working Copy
image2016-3-6 16:2:5.png
SourceTree is a very good stuf.
Thanks