yeah, a lot of what the course is teaching is being able to create 3d appearing images on a 2d surface. So although the mechanical elements might not transfer completely your arm thats doing the drawing is still going to become more coordinated. your understanding of form and construction will improve and that will translate to any medium you choose to work in. uncomfortable wrote a whole article of why he believes it important to use ink, in summary from what I remember it encourages you to think before making a mark and becoming alright with making mistakes and working with them.

 If I remebmer correctly there is an article here adressing you concerns in faq section. In case you already read it I will share my opinion. I think the skills learnd in these lessons are essential basics. That makes them very trasfarable to any medium. Trough these lessons you train mind-muscle connection. After training you are able to execute the moves you intend to in your head more accuretly. That should also apply to any hand movements you do to draw on tablet. In addition lessons should improve your analitical observation skills. I believe this gives you more freedom to draw whatever you want, however you want. When you are able to understand forms you can manipulate them more easily and it alows for more flexibility and creativity. 

 I myself started not to long ago so I don't understand or know much yet. Still these are reasons I keep in mind when working up motivation to do this course, so I thought I'll share them. :)

You can draw from the shoulder on any size tablet. It is about freedom, control and confidence in controlling the pen. However that is a bit of an aside.

Consider that drawabox is is tough and takes a real investment of time to do properly. If you wish to pursue it I would recommend getting a stack of A4 copier paper and some fineliners. The digital bit is fine for your own art but not for the course.

I use tiny tablets because I don't have space for anything larger than a small paperback book on my desk and as I've done DAB I've found myself using my shoulder for long lines that I want to get straighter and the like.

The only time I've found myself restricted to ONLY wrist movements is when I have "mouse mode" (sometimes called "relative mode") on versus "pen mode" (aka "absolute mode"). The pen mode has a 1:1 comparison to your screen where mouse mode works just like a computer mouse. I used to use mouse mode but recently switched to pen and my wrists have thanked me!