Hard to answer in general. The one I linked to was the latest development build at the time, and one I am rather confident does not break anything.
We try to not introduce any bugs into what is the main development branch (known as the master branch, you can see the word “master” in the page I linked to), but during development all things can break. And some of the builds there are also for specific features in development, and those can be incomplete or even really bugged at times. So if you try any of the development builds I usually would recommend using only those that indicate being for “master”. And using the dev builds is definitely at your own risk 
You mean never overwrite existing cover art? Unfortunately not at the moment, but yes, it would be good to have.