The cichlid specific substrates I've seen were all buffering substrates for African Cichlids. The shells in this mix are a goor indicator that it is going to buffer the water and increase the pH. If you are planning New World Cichlids you'll probably want something more inert.
danios are target fish. I put them in with my angle so the angles would go after the danios and not eat my community fish before I made a strictly angle tank.