I am partial to Logitech keyboards, but am a typist and not a gamer, so I don't use mechanical keyboards (yet). I was wondering what makes one membrane keyboard cost $30 and another $60+? As an example, I am now using a Logitech K270 (a decent keyboard but not unified USB), and looking for another Logitech like the K750. What's in it that makes it more than double the price?