This six minute video shows how to use this plug if the pdf has left you a bit baffled.
http://www.borisfx.com/videos/BCCFxPlug/Motion-Key.php
I think you can find a video or tutorial for each of the plugins in MS 13 if you look hard enough on the Boris site. Again, I think these have really added a lot of power for many of the common issues in my videos.
I have noticed that we got subsets of the Units Plugins and not full ones. Probably these are 3/4 of the number of plugins in the commercial Boris FX stuff. But still for me very useful stuff.