I've had both, I'm a web designer, I much preferred the microsoft one, the K400 felt much cheaper and clickier, I'm normally a logitech fan, but the microsoft one seemed more durable to me and I preferred the more tactile feeling to push the keys, the trackpad is good and the buttons underneath are physical they are just not raised.
Bought a K400+ a few days ago and love it. K400 has physical mouse buttons whereas this doesn't. Easy choice for me. Hot for the reduced price but Cold for not having physical mouse buttons.
Damn bought it two days ago lol
Ordered this last week, returned to Amazon yesterday. The keyboard is advertised as a full size keyboard, but it really isn't. The typing experience isn't great, keys are too 'mushy'. The trackpad is a major let down too, it starts tracking movements only after you've already moved slightly. Tried to live with it for a few days, but the control is very frustrating. As many say, the Logitech is a much better alternative, though the keyboard on it is a tiny bit smaller than the Microsoft all-in-one.
Had both of them some time ago, returned the Microsoft one. Better feel of the keys, better durability, better touchpad and connection and so on.. get the Logitech K400+!