Input Mono vs Hasklig

Although font designers need to make money too, open source model is preferred.

This can be a pro or con depending on who you ask, but it would be nice to have the option.

This often impacts upon designers working with hexadecimal numbers. Many fonts address this by either changing the x-height for numerals, making "8" more of an hourglass shape, or making the "B" cap smaller. At 10 pt, there's less than three pixels of a difference (anti-aliased).

A lot of decimal digits have a similar form, 2's can sometimes look like 8's and so forth, which makes long strings of digits hard to read. I find other fonts like Consolas's digits more legible even at smaller sizes.
In the proportional variants this is less a problem.

The dot is so close to the body that they fuse, and with the serif on top it looks like the cap of the letter "1". When you put them side by side it's easy to see which one is which, but if you see a code that reads "a+=i" you're going to read that it increments a by 1.

Tilde is basically indistinguishable from a dash, unless you blow the size up huge. The curves in the tilde are too shallow.

Some coding fonts with ligatures, like Fira Code, turn != into ≠, but Hasklig does not. The reason for this is that Hasklig was designed for Haskell code, and so turns /= into ≠ instead.

Unfortunately, not supporting emacs is the number one reason I don't use this font all the time.

You want to see exactly what you've typed, not have your brain have to do a little dance every time you see one of these artifacts.