It was a maddening guessing game, where occasionally - but not always - the edge of my lower thumb would touch the track pad and send the mouse pointer warping off to some other part of the screen while I was typing.

On the previous one that OP is talking about, you had to guess. On the new ones just announced, there are physical and visible lines.

It is slightly wider than the space bar. I've never had an issue with mine, as it is located exactly where I expect it to be.