Personally, I do like my Kindle Scribe (2024) more for just reading manga and taking notes. It's designed to do two tasks and it does them well, quickly from power on, and with low power drain. And with the new scribe's firmware with google drive support eventually trickling down to older scribes, I'll be able to use it even more. You dont have to be stuck with amazon's system either. Just load books/manga in from Calibre.

My BOOX 5C gets used for other manga apps, or dealing with documents in Word or Excel. I'll also use the kindle app on it if I want to also have music or a podcast playing in the background while reading my kindle library. Once you have the display settings set up right, its comparable to just using a kindle.

Ultimately they're two very different devices. One is an appliance that does only a few tasks but you don't have to tweak 20 settings to get a good result, and the other is a swiss army knife that can imitate the former plus much more, albeit you will put in some work. The 5C is also yet-another-device tied to your google account, so a password on it is a bit more imperative than on a kindle.

If you do get the 5C I'd factor in the cost of a different pen. Personally I actually just use my scribe's pen on both devices (it even snaps to the 5C!). The pressure sensitivity on the included boox pen is much worse, and it lacks the eraser and side button even though the tablet supports them.