The actual unit looks just like the ones on ebay sold as 10 and 20 gallon sandblasters for half the price. The soda is the media, cost seems about the same as glass beads. If you're going to paint the surface you don't want a smooth surface, you're better off with the "etched" surface produced by grit blasting.
soda blasting is commonly used on fiberglass, ive seen it used on a lot of boats and its very gentle but does an excellent job metal too. i was considering buying one