First of all, as soon as you proceed to purchase the license, you get to see something mentioned like this below the header-
"You Are Purchasing iMyFone TunesMate for Mac" or "You Are Purchasing iMyFone TunesMate for Windows". Simple, if you are willing to use the TunesMate on your Mac, download the Mac version and if you are willing to try it on Windows, you can go for the Windows version. Rest assured, it works miraculously well on both.