The Aura One is essentially perfect. The only gripes I have are the USB port and non-removable battery. It is a bit slow with the stock OS but with KOreader it runs amazingly well.
There's something to be said with a device that has a single purpose and supports custom firmware: other than the micro-USB port and the slightly shorter battery charge I don't think I will be changing it soon.
B/W only, thin in the hand, simple interface, PDF transfer via USB.
I think most go this route for comics, graphic novels and some read magazines on it. Niche, but not a gimmick.
Biology spent a ton of time adapting and evolving for the ability to see color but sure, it's a gimmick. I guess you should consider syntax highlighting a gimmick in code editors as well? Charts/graphs in textbooks use color as a gimmick, any book that include illustrations/images in color are gimmicks
When we went from black & white photography to color photography we also introduced a lot of tradeoffs. Would you have considered color photography a gimmick ?
It sucked or was massively inconvenient for the first 50+ years.
Right now - on smaller devices focused on books like 6-8" Kobo/Kindle devices this is primarily a gimmick used for book covers and perhaps some text highlights at best. That's what makes it a gimmick, especially since it comes with such a massive loss of contrast that you need to drive the backlight at 90-100% during the day to get readable experience out of it.
And I'm happy that Kaleido 4 improves this (it's one of the things I'm most excited with for my 10" Boox where color screen is much more useful), but even with 50% improvement the contrast is still significantly worse than on the BW readers, making the experience of reading normal books a significant downgrade in exchange for some color front covers.
Your comparisons to TV are just inane, the tradeoffs aren't even remotely similar. Noone is clamoring for rainbow letters on their Kindle.
> that you need to drive the backlight at 90-100% during the day
Well, okay that's objectively false and anybody that has used one or owns one can tell you this.
That said, of course if you want to view color content on an EPD then it is quite necessary and not a gimmick at all.