PN
Kindle is not my choice, for various reasons.
I have a Hanlin V3, but also very much like this one, which has the benefit of a discount on the titles.
COOL-ER ereader for ebooks from COOLREADERS
On the cost benefit analysis, it is the ability to carry multiple books that does it for me, as I have a library of reference books and standards for work and carrying 30-35 books isn't an option
I have never calculated the payback period, but can see where you are coming from.
My gilet has two deep pockets on the inside, that wil take papers and books.