Awesome @regrog! Sincere thanks for the feedback 
I’m relieved it didn’t break on you. Heh-heh.
I did that primarily because ${projectDir}/build/classes... is a Gradle convention for the output folder. And since mrJar is a Gradle plugin, it makes sense to me to follow that convention.
The Gradle convention thing is the primary reason I went for build/.... But secondarily, it’s just a habit I’ve developed over a lot of years of using Eclipse. I just always nuke bin as usually the first thing I do whenever I create a new Eclipse/vscode project. And replace it with either target/classes or build/classes. Depending on which builder I’m using.
I’ve done it forever and it’s never caused my Eclipse/vscode projects any problems.