Non-vacume ported spacers for carbs in hight?, type?, material, and gains?

Hello All,
More questions and what if's for spacing carbs. When searching on this topic I didn't find as much as I expected, there was more toward ported and adapting.
So my understanding of this type of spacer for both 2bbl and 4bbl of any type is this.
Hight - Effects Atomization of the fuel (the higher the better, to a point)
Type - Being a full open strait bore, individual bores per port, individual bores per port with horn or spiral machining
Material - Aluminum (best), polymer style (mid range), or wood (basic original)
Gains - Increase in top end H.P., better fuel economy
Am I correct in my understanding of these type of spacers?
Does anyone use these spacers or does anyone have a particular recommendation?

Chad