kJams is “Shareware”. That means it’s completely free to download and try! In fact I highly recommend you try it out before buying.
Note that the until you purchase kJams, it will be in “Tryout Mode”, and it will have some limitations. The “Tryout” and the “Licensed” versions are the exact same application, it’s just that the licensed version has been unlocked, so it is no longer in “Tryout” mode.