The quality of the filter absolutely makes a difference: the tranmission quality of the glass, whether or
no the actual colorizing of the filter affects the light path, the flatness of the glass, and yes, the nature
of the coating. Not only if flare an issue, but sharpness. How much this matters is related to how well
you've otherwise controlled flare through proper shading, and how much enlargement the neg is going
to need. With color film, there are some additional variables. Whenever possible, I only buy multicoated
filter for a high-reputation manufacturer. Hard multi-coating also have an additional advantage: they
attract condensation and chemical outgassing vapors much less. This can be a big deal in the field.