I may be utilising it wrong but shouldn't the output of $base-spacing remain relative to the base font size of the project (font-size on body) and not the font-size of the current selector? Therefore wouldn't rem be a better option here?
It depends, but I tend use em’s for this, and I don’t think there is a right or wrong way, here. But Bitters is meant to be changed to fit your needs, so feel free to swap em for rem in your project.
I may be utilising it wrong but shouldn't the output of $base-spacing remain relative to the base font size of the project (font-size on body) and not the font-size of the current selector? Therefore wouldn't rem be a better option here?
Obviously no IE8 support.