Hmm, I've used a coir-based mix (without polymers) for seed starting, but I heard somewhere that polymers weren't recommended for food plants. The manufacturers recommend their products for everything, though.
The X-Pand Garden Soil website says, "Moisture Boost Plus™ Coir is naturally more water absorbent than plain peat moss but also allows the nutrients to slowly be absorbed by the plant. Plus we add Water Smart™ crystals that hold moisture and release only when the soil starts to dry out."
"Water Crystals polymer is odorless water-absorbing polymers (polyacrylamide)"
http://www.crystals.us/index.htm