Got tired of the damn K400 only supporting ONE multitouch gesture, and Logitech's half-baked software implementation (even being generous). No middle click at all, no right-click gesture. Tap-and-drag doesn't work well (it starts dragging only after the arrow has moved a few pixels, which makes you select text incompletely, or resizing windows very annoying, for instance).
The Rapoo I got at Walmart online for about $35. Build quality is pretty much the same as Logitech. Pretty much all imaginable gestures work (even in W7) without installing the software, which is only necessary to change default gestures (which the K400 never gave the option to). 3-finger middle click, 2-finger right click, 3 finger swipe down to minimize/restore, pinch to zoom, all work, out of the box, no software installed. Keys are actually full-size, while the K400's are smaller, and the trackpad is bigger. It's only about a cm longer, but significantly less tall. The right shift key is the correct size, and it works in the 5GHz range instead of the cramped 2.4GHz one. The only pet peeve I have is that there's no triple click, but that's minor compared to the plusses.
I can't believe it took all these years for a company to put a simple product like this that just worked. Logitech could have very easily done it with the K400, but they never even came close. Now they sell a new, slick, very expensive model though.