I've been using it. It has a very good calcium content, but for me it is too low in alkalinity. However, a 50/50 mix with Reef Crystals is perfect! The 50/50 mixture comes out at 430-450 ppm calcium and 145-160 ppm alk, sometimes I still need to supplement mag, but not much. It is slower to dissolve (kinda like the Tropic Marin Pro).
PS - I did get a damaged bucket from Foster and Smith. They replaced it and didn't even make me return the damaged bucket.