i find it to be difficult to select small pen sizes, its not easy on a tablet
while one often wants a line exact 0.5 1 2 3 4 5 6 7
Although the slider is nice, pens often have a contact tip that inserts a bit making it difficult to use the slider.
maybe some extra panel for those small exact pen sizes.

(i dont know for a mouse as i dont have a mouse on my labtop)