The amount of nitrates, nitrites and copper are extremely low and about what is normally found on a reef. Instant Ocean and other mixes normally have a bit more copper than found in the ocean. However, they do not have Nitrates, Nitrites or Ammonia and normally a very low (not readable by standard test kits) trace of phosphate. Instant Ocean is also known for have a higher than average ph
levels (about 8.6 on my tests).
All that said, I still use Instant Ocean because we are talking parts per million and are are all naturally occurring in the ocean. I am sure that I am not the only one using Instant Ocean and I am not the only one successful with all types of inverts.
I could not find pricing on the Catalina water, but I do not think your fish will notice a difference between a mix and real saltwater, but you wallet might. Keep in mind that we are buy fish from all around the world and parameters that are perfect in one place could be way off another. There is not a "Perfect Solution"