I have a 4 piece aluminum grinder I bought on ebay for $12. I'd rate the quality high, since I also have an $80 Mendo Mulcher for comparison. Mendos are generally considered to be the equal of the Space Case, and are preferred over the SC by some. The no name has good weight and a nice screen, which, unlike the Mendo, gives the pollen no crevices to hide in. The Mendo is a better shredder, but at 3" in diameter, vs. 2" for the cheapie, it has larger holes and grinds the herb to a consistency more suited to joints than most vapes. So I'd say the size of the grinder and its holes has as much or more to do with consistency as teeth sharpness or placement. Processing my herb a 2nd time through the cheapie gives me the fine grind I need for the SSV and PD. I also capture quite a bit of additional pollen the 2nd time through, which makes sense. I bought the Mendo for faster and higher volume grinding. It satisfies there, but can't do the trick with getting it fine. The two work very well as a team though.
there is a big diffrance in potency while vaping between finly ground herb and not so finly ground herb.
If you're applying that statement to all vapes, I think most people would disagree with you. It may be true for a particular (and inefficient) vape, but certainly not for all. The herbalAire is a good example. It's as efficient as anything on the market and you don't grind at all.