Probably in a few years this whole debate topic will seem quant, as devices will be much at figuring out when we're addressing them than the primitive idea of a wake-word. :-)
But of course its much easier to require "Hey"
i bought an echo dot on a whim, since it's so cheap, assuming it'd be fun to play with, but not very useful.
to my surprise, it's really handy. setting timers, adding food to the shopping list, and playing music are all super-convenient with alexa. turning lights on and off with her is fun too, although i admit, it was already a fairly easy task to do using a conventional, physical switch. :-)
Amazon tried to get around it by naming the product "Echo" while making the activation phrase "Alexa" but that means people don't call it "Echo" in practice.