Using pen on paper is much more natural, tactile and much more efficient in terms of concentration and uninterrupted work for me.
YMMV, of course.
On the other hand, the second version costs $500, a luxury purchase for many people.
However, e-ink lacks speed and color. The papers I read use a lot of color in diagrams and waiting for e-ink screen to refresh, reduce its color palette to accelerate and re-refresh to return its previous mode is both distracting and flow breaking for me.
Also, I use a lot of colors for different things on paper. Different highlighters for different stuff (yellow for "further research", blue to "remember this part"), etc.
iPad with Good reader is almost as good as my workflow but this thing is heavy, backlit screens are eye-straining...
Since PDFs are not made for screens it's also distracting to zoom and scroll too.
So we need another format (maybe ePub) for academic papers to read them effectively on digital devices.
Though I did order one.
While I love to read and write on paper, I don't buy any paper books anymore.