Re: Poor product design?
Haven't used the K4 so can't tell how different the page turn buttons are ... on the K3 they are very easy to use ... but this also means I quite frequently press them by mistake!
Loss of keyboard is no big deal for me - I think I'd see it as an improvement. The number of times I use the keyboard on my K3 is minimal - and if I am using it I tend to need the symbols as well which is a on screen select by arrow keys affair and in any case the keyboard isn't suitable for any serious typing.
Not getting an AC adapter - hmm, my Kindle charger is now my micro-USB charger of choice as its (a) very small (basically a 13amp plug with a USB socket) and (b) is a different colour (white) from all the other chargers I need to take anywhere so its easy to find in the "charger bag"!
That said, there's no need to "upgrade" from my K3 to a K4 ... but if the Kfire arrives, that might be different.