When comparing Monoid vs Operator, the Slant community recommends Monoid for most people. In the question“What are the best programming fonts?” Monoid is ranked 28th while Operator is ranked 52nd. The most important reason people chose Monoid is:
The common expression '!=' is displayed as '≠', '>=' as '≥' *, while maintaining the fixed width double-space that these characters would normally take, so as to maintain text alignment. * Many others are supported too - see site for details.
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Pros

Pro Novel use of ligatures to display ascii character combinations as symbols
The common expression '!=' is displayed as '≠', '>=' as '≥' *, while maintaining the fixed width double-space that these characters would normally take, so as to maintain text alignment.
- Many others are supported too - see site for details.
Pro Open source
Monoid is open source meaning it's freely available to anyone.
Pro Sharpness
Pro Customisable
The user can adjust letter-spacing, line-height, and choose alternate characters prior to downloading.
Pro Has a script version
Operator can be used to mix the same font for syntax formatting.
Pro Horizontal width not as wide as other fixed width fonts
You can legibly read everything and get more characters per line.
Pro Super readable
Long strings can be read in Operator exceedingly easily. The font just flows nicely, with all the benefits of clarity that provides.
Pro Adorable italics
Cons
Con No bold-italic style
Monoid doesn't offer a style that is both bold and italic.

Con Relatively expensive
At $179, this font is on the more expensive side.