Been using water crystals for years for outdoor growing. They work great. You will get more growth. They not only increase available water with the rains but they also tend to keep the soil looser and more airated by expanding and contracting. You can use up to about 1.3 times the recomeded rate with no trouble. Turn them into about 5-6 inches. Don't overdo it though, as there is a definite best / max rate. Over that and you will end up with a big jelly like mess after a rain.

good luck

BTW - any cheap brand will do its all the same stuff. Can get it at any garden center.