http://valinet6l6tq6d5yohaa6gdsf2ho4qcqcxyj2nahp5kd4z7nsa6ycdqd.onion/2015/09/22/ThinkPad-W540-review.html
This particular model clicks in in its entirety. You can press anywhere on it, and it will perform a click. I configured mine as one giant button, so I can left click by pressing with one finger, and right clicking by pressing with two fingers, and scrolling by flicking two fingers on its surface.