Made of what is essential bubbled glass formed in volcanic eruptions pumice is the best ammendment for succulent soil.
The superheated rock forms tiny air bubbles in the rock which not only increases aeration it also provides increased water regulation by allowing water to flow through (unlike sand or other grit additives).
While perlite can also perform the same aeration and water regulation as pumice it is so lightweight it often "floats" to the top of your soil providing neither of those functions. It is also so easy to compact you can crush it with your fingers.
Our pumice is approximately ⅜" size (at the largest) which make it an ideal size for amending pots large or small.
Small bag is approximately 14 oz (would fill up three 4" size pots).
Large bag is approximately 25 oz (would fill up five 4" size pots).