>Joe
Audacity applies the effects to the file, which can then be saved in its new form. The basic tempo and pitch adjustments cannot be made when the file is being played, so it is difficult to assess their impact without doing some maths (there are some new effects which do affect play-back directly, but they seem a bit complicated!).
Slow-Downer and s8 apply the changes while the file is being played, so it is easy to adjust to sync with other material, or to the pitch of your squeeze box. Or just to play along with slowly. But s8 saves the modified file in real time while it plays it, so you wait a long time; and only into its own folder, which may not be convenient. I don't know much about Slow-Downer.