Slow motion is a very useful feature, and it works for any video or audio mp3 in the Pro Player. Using it is very simple.
Select your desired speed using the "Speed" controls. For any course videos, or any audio mp3s, there should be several choices ranging from 50% to 100%. For older Free Lesson Friday videos, there may only be two choices: 100% or 50%.
This option may not work on smartphones that force video to play fullscreen. However, on any modern tablet this should work fine.