This is one of those plugins that I don't quite think is ready for prime-time. I tried the free version, and thought it would be better - but to be honest, there's not a huge amount of difference.

When using playlists, you don't really get much in the way of customisation - like being unable to remove the download button from the player.

When trying to activate it, it says the license code is incorrect. Removed the added spaces at the beginning and the end and still no luck.

Switching over from free to pro meant that I needed to disable the free plugin first as Wordpress threw an error - it would have been handy if the plugin had automatically deactivated it. It also showed an annoying nag about importing the free version files, which I couldn't get to disappear.

If you want playlists, default player customisation etc - then go for the pro version. Otherwise, stick with the free plugin.