Thank You for Your reply and some insights.

I have experimented with my own variant of The Everbook. I discovered it last year and played with it for some time, and recently I have found myself liking it more and more, because of its portability. I have made my own version of it: in size of A6 format, which suits great with my note cards (I still keep my Zettelkasten-ish catalogue of different notes), and made of hard paper from old paper folder. I folded a suitable slip of paper, attached an elastic band and it works fine. I like it, because it feels like a codex, but work like a box full of loose cards.

I call it a prototype of my own version, because at that time I was not sure if I want to use it, and it is not quite The Everbook per se, because when I have discovered it at first time there was not any product for sale, now there is, but it is too expensive for me. On a dedicated YouTube channel there are videos of different people with theirs variations of it – they used different materials, and had different ideas. So now I consider making my own leather case or whatever material I will be able to get. I have even thought about partially implementing something called The Handi Desk (check this out too, by the way), and making something with these two concepts.

I consider The Everbook more as container for cards than productivity system or something like that. I have my own folders in it, and I already developed my own system of making and managing my notes, so I do not need any new approaches, but I was looking for something to carrying cards with me when I have no access to my main box and something between commonplace book and Zettelkasten (some book with pockets, where each page is like pocket for another notes and pages), so The Everbook, or my version of it, I should say, is great for me for now.

I think it is a very handy way to carrying daily or casual notes and other things along, especially these which can be processed without a whole system of notes.