It's a great product, in that it does what it says it will. For a small tank, it's a good way to maintain the right levels and balance of calcium and alkalinity. Because it's in two parts, you can add more or less of one component if your parameters are out of balance.
In a larger tank, it can get expensive to use, especially if you have a lot of stony corals. Even then, it can be used as a supplement to kalkwasser or some other less expensive additive.