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Capacitive is cheap. Maybe the cheapest. Some older touch eInk screens used IR because it doesn't reduce the reflected light. The Capacitive and Resistive screens have additional layers which slightly reduce the light. Part of the reason why most now have front lights.
The original Kobo Aura H2O used IR, which is why it has a whiter screen than the Libra (Capacitive). With no front light it's the brightest of PW3, PW4 and Libra.
I've used older eReaders such as Sony PRS350, Sony T1, Kindle DXG, Kindle Keyboard, Story Cover, Nook Simple Touch, Kobo Touch (C version). I don't know which touch technology the Touch ones use, but all are greyer than PW3, PW4, Libra, H2O etc because they are older design of screens, the non-touch models being mostly the oldest.
Oddly the worst I have is the Kobo Touch (C version), but that's due to worse ghosting than any other eInk screen I've seen.
IR may use more power than capacitive unless clever programming is used. I suspect to mitigate it that the scan LEDs on time and speed is reduced till a touch is detected. You can see an initial delay on the sketch application on the original H2O. Capacitive can be very low power. IR uses a row of LEDs on two edges and a row of phototransistors (or diodes) on the opposite two rows. The black plastic bezel, or black layer under the bezel is transparent to IR and is a light pipe and set of lenses.
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