This. I use it all the time. Every character is fixed width except 'm', 'w', 'M', and 'W', which are 150%. It mostly looks and behaves like monospace, but with a very nice minor adjustment that makes it more readable and pleasant.
m, M, w, W, %, @ and i, l, ! (and so on) are the letters that create a challenge (or a room for creativity/individuality) ad they are so wide or so narrow. Wide letters often get cramped as they need to share se witdh as narrower letters. iA thought they could just modify those “extreme” glyphs to increase legibility (and readability)
https://github.com/iaolo/iA-Fonts/