My Book MAC compatibly

I am looking at the My Book external hard drives and see that they are Mac compatible but am wondering if they will work with macOS Mojave out of the box or do I have to format the drive?

New My Book devices come in exFAT file format supported by Windows OS as well as macOS but required to reformat in HFS+ to use with Mac Time Machine. While old My Book for Mac devices already come pre-formatted in macOS compatible HFS+ file format, so no need to reformat.
You may check the following links to check the file system details of new My Book and old model My Book for Mac: