Most other pixel art programs I’ve used that had such feature, simply don’t let you sometimes put the line you want when it is enabled. It’s hard to describe, but it makes it feel clunky. PM, however, dynamically recalculates the line in kinda predictive way so you always draw what you mean to draw (I was able to make a fairly regular heart 1px outline which is pretty hard to me in most software with pixel-perfect drawing and I didn’t even try much to do it), which I think is great.
Didn’t really belong to other categories so putting it here as I just wanted to share that bit of praise. Feel free to use it as user testimony for advertising purposes if you want.