To preview the MP3 file you must install the Flash player.
The both licenses include the permanent right to use the audio in any number and types of applications. The only difference between them is the price, but it is set still very low even for commercial projects.
You are buying the non-exclusive right to use the purchased audio in your project - like brand promotion video, product promotion video, podcast intro, freeware games, non-commercial documentaries etc.
You are buying the non-exclusive right to use the purchased audio in the work you are selling - like After Effect templates, commercial PC /Android/iOS game, commercial video, etc.