In my neck-of-the-woods, we don't have the luxury of native rock. As a result the cost of matrix cubes over rock is not that much of an issue. Given the propensity for rock filled basins to clog in high organic load locations at a faster rate than matrix cube applications, the use of these blocks is a no-brainer to me. Additionally, when matrix cube basins do clog, they are much easier to flush and clean than a rock filled basin.
"Everybody is ignorant, only on different subjects." - Will Rogers