How is it different from just pressing "t" on the project's page?
Click a line, press y, and it changes to the commit where that line was last changed. Since it shows the tag the commit applies to up top, it's relatively easy to mark what release was affected by a specific breaking change.
Based on the feedback/usage I hope to build more features like goto method/variable definition to make it a more complete product.
Github's keyboard shortcuts are nice, but there is lots of room for improvement in how you navigate code.