I suspect that like many people NT221 is my first proper experience of Logos' Mobile Education, as I picked it up on a community pricing at a much more reasonable price than normal.
All I'm going to say is that if it was Logos' intention that picking up NT221 on the cheap would draw me in to spend megabucks on normally priced Mobile Ed packages, then it's working! I can certainly see the value much better. With all the required and 'see also' reading, there's going to be at least a couple of months worth of value for me from this one resource.