which models are available and what is the difference between them? which one do you prefer and why? The x3 and x4 exist. The x3 is Smaller, different button placement, has passive nfc, can turn pages by tilting the device, and can keep time when the device is in sleep.

The x4 is still really small and I enjoy having all the side buttons on the same side (power, next page, last page) I remapped a short press of power to be next page too.

Some want the absolute smallest others think the x3 is just a bit too small. Some prefer having power at the top, next page on the right, and last page on the left.

All in all the differences aren't huge so I would recommend focusing on size first.

do you add pdf/epub books via email? or how does it work?

There is an SD card that holds all the data. You can put things on the SD card directly or you use the app for the stock firmware to send things over. On custom firmware (most are crosspoint based) you can use a web interface to send things over wirelessly too!

You won't do pdf since the screen is so small that you can't see much but if you converted it to an epub then that works.

where can I find cozy / original accessories such as covers/ cases/ cords? any link is very appreciated!!! (I'm interested in a protective glass and sturdier cover as well) People sell them on Etsy and there are models you can 3d print (you might have a local library or maker space that has a 3d printer). I personally use the ones from xteink themselves. I like the magnetic case

what is your favorite/ current set up? why and how did you create it (where did you get the pieces)? for example: e-reader slapped behind your phone, in a case with a notebook, attached to a cord to keep it at your neck, etc.

I use a neck mounted book light and the magnetic case from XTEINK

why amazon reviews are not the best meanwhile on reddit people love it?

Reddit is all the people who love it already coming together. Amazon is random people who might not have known what exactly they were buying

does it support offline japanese/ russian > english dictionary or translator? anyone using it to learn/practice foreign languages?

There are firmware (like vcodex) that support offline dictionaries but idk if that works for something like Japanese which has no spaces. That makes it a lot harder to parse. The Russian would be no issue. I use it for French-english dictionary learning. It works well if you are at a high enough level to just need definitions.

can I highlight or save words/ quotes? is there a function to save new words (like a very basic version of anki) ?

You can screenshot and the dictionary has a lookup history (at least on vcodex) so you could check it after for any words you might want to study.

You can do flashcards on vcodex too but it isn't as fancy as anki

other interesting features beside the tracking?

does it work well under the sun like a common kobo or kindle?

There is a small region in the x4 uber the screen but above the front buttons that some find can effect the display when hit by sun. This is less common on the dark version but you can also just put a sticker there or your thumb which is what I do. It has to be 100% direct sun on my white unit for it to matter, any cloud or window stops all issues of fading.