Too many, indeed, yet all the same....
I've lost count of the 6" clones, and I don't care. The size is too small for immersive reading and the screen is basically the same old thing with marginal contrast, that I am getting tired of.
Methinks, until you have color, and good color at that, and large enough sizes to have a hardcover experience, and to be able to read larger format, complex layout publications, ereaders will remain a niche product.
Until then, I don't see anything new under the sun, except a race to the price bottom for 6" devices.