Difference w/ SWFTools & FileField?

No dependency on SWFTools.

That may be true, but this seems to be a dedicated module for an audio only field. So like many of the Drupal solutions, it's all how you want to approach it for your personal tastes. And I'm not the maintainer either, so there may be more technical advantages as well. You'll have to see if they reply here.

I would migrate from SWFtools if I see some kind of play statistics integrated.

Audio field only plays music and has less options. This means your site looks cleaner, from an admin POV, and it is quicker to learn. On the flipside SWF tools has more features and can play video.

I like that it's a dedicated audio field for CCK. It's nice when something does one thing well. Makes life simpler sometimes. That being said, Drupal itself does a lot of things well, so having components that focus on a single function really simplifies the process. Usually the developer can excel by focusing as well. That way we all benefit. However, I did switch to SWF tools when this thing didn't work, and from a viewer perspective they would never know the difference. But adding a feature like a play counter would be helpful. And if the implementation of this module were just drag and drop then it would be especially useful by reducing the time it took to implement a working audiofield vs. the complexity SWFTools brings with it due to it's multi-functionality.