Ranked in these QuestionsQuestion Ranking
Pro Great readability
Equally well readable as Bitstream Vera/DejaVu Sans Mono, but with slashed zeros (aids with legibility).
Pro Easy on user's eyes
Characters are very readable. They have consistent widths across all weights as to not break up words. Commonly used programming symbols such as various kinds of brackets are made easily discernible from each other and various punctuation marks are made bigger than normal. This makes them especially good for programmers who keep staring at code for hours.
Pro Clear differentiations
I, I, L, l, 1, O, 0, etc.
Con No bold version
This is not so great on a dark IDE, the characters tend to wash out, unlike something like Consolas.
Con Seems too wide at size 16
The letters become quite wide at size 16, impacting upon readability.
Con Doesn't work at size 10
Menlo displays as expected for size 11 and bigger, but doesn't seem to work very well at size 10. Issues include zero not being the same height as the rest of the numbers and Parenthetical Brackets not matching up perfectly.