All the cheap KVMs I've tried only allow for a 2-button mouse w/ scroll wheel function, and a standard 104-key PC keyboard. Any other buttons or special features are blocked.
The nicer KVM switches with keyboard+mouse+USB hub ports will pass through the keyboard and mouse exactly as they are, but only if they are plugged into the USB hub ports of the KVM, and not if they are plugged into the dedicated keyboard and mouse ports of the KVM. The downside to doing this is that the keyboard/mouse act like they are unplugged/plugged in every time you switch, so there is some delay when switching before the keyboard/mouse are usable again. (If you use the dedicated keyboard/mouse USB ports, there is typically little or no delay because the KVM switch is keeping an emulated KB/mouse connected at all times.)
Of course things are always improving, and I haven't tried the exact model you intend to buy, so it's possible that it will work better than those in my experience.