Initially I wonder whether the download file is the "design" or just a "representation" of the gear in question. i.e. is the tooth surface simply part of an arc that is "close" to the involute surface? Also with low tooth numbers, there is a natural undercutting in the tooth root. Is this correctly reflected? If not, there will be a tip/root interference and a "clunky-ness".

Mind you, from the roughness of the surface of 3d printed parts that I've seen, the above is irrelevant!

Two pinches of salt from me.

I'de just buy the McMaster version (or similar)

-Martin