Used to use it. Same deal as the last guy in terms of procurement.
Always mixed to exact numbers every batch, provided you weighed the ingredients correctly. The problem for me was that I could never seem to get it to keep alkalinity or calcium higher than the minimum recommended ranges for a reef tank. My growth was non-existent, and when I went back to IO, the growth exploded. I literally had two years with no growth on ESV. The entire time my tank was lit with 20k 250w Radiums.
Now, I know many successful reefers have used ESV, but after two years of no growth and switching back to much cheaper IO (after I literally exhausted every other variable I could think of), my personal experience was that it wasn't worth the money.