Instant ocean is not bad, made by the same company that makes reef crystals. Reef crystals just has more added minerals (calcium, magnesium etc.) so for a few bucks more you just have to add less supplements.
As far as crystal sea marine mix goes I tried one box a long time ago and did not like it because I mix all my water in white 5 gallon buckets.
When the salt was dissolved in the bucket there was a relatively large amount of undissolved dark particulate left in the bottom of my buckets what this foreign material was left doubts in my mind.