Many growers don't realize the importance of calcium. Your plants cells cannot divide without it, which means it can't grow without it. Calcium is essentially rocks which gives your plants the strength they need. The community seems to be in a consensus that CaliMagic is the best. Personally, I have no idea why anyone would buy it.
Pro's- Most popular among growers
Con's- It's watery most calcium sources I'm used to calcium sources that are thick like milk or rocky like bones, shells, and rocks. Magnesium isn't really needed that much, Epsom salts will get the job done. I've had weak plants with branches that took days to recover from supercropping.
Pro's-Thick, smells great, can be used as a flush, makes the strongest plants I've ever seen. Supercropping was more like bending it multiple times just to get a little movement. I've taken over sick clones and after a few weeks grab the top and bend it below the pot rim let go and see it fling right back into shape.
Con's-if you use a little too much, height seems to be inhibited
Cost Comparison- We'll use the 2.5 gallon size for cost comparison and monstergardens.com for pricing. General Hydroponics CaliMagic runs you $67.90 and Nectar for the Gods Herculean Harvest is only 49.95
My opinions are based on my experience in farm and commercial greenhouse growing