I actually might not trust the $3 carton of epsom salts from Walgreens (although I've used it in the past, foliarly). I would be concerned about applying it to soil for one thing, and I do prefer using products that are intended for horticultural use.
What I mean more specifically is that although it says "Derived from magnesium sulfate" (or whatever), there must be more to the manufacturing process and a more complex mixture of minerals than just magnesium sulfate from epsom salt inside that bottle. Of course, I understand that they have to protect certain information such as the blend of source materials used and any proprietary processes behind it all or risk opening the door to imitation products. Luckily American Agritech does provide an informative brochure about their Organicare line on their website, but you'd only know if you looked and even I almost didn't even notice the link to the brochure.
The origin of ionic minerals
Minerals are created from the oxidation of organic matter. Most Ionic materials are a fracture of extracted
Humic substances from brown lignite. The oxidation process creates a product that has a high carbon and
oxygen content and contains large amounts of free radicals due to the high amounts of oxygen - hydrogen
groups. These groups are vital in the electron transfer, which is important to ionic exchanges.
How Huvega works
• Releases minerals in soil - Huvega solubilizes substantial amounts of minerals in the soil and can enter into
complex bonds with various dissolved minerals.
• Protects plants from stresses - Huvega aids in the relief of oxygen deficiencies, which increases the
resistance to drought and other environmental stresses.
• Stimulates antibiotic protection - Natural antibiotics such as streptomycin, terramycin, and penicillin are
produced during the decomposition of plant residue. Huvega and other phenolic substances enhance the
uptake and translocation of such antibiotics in plants.
• Reduces wilting - Huvega helps the plant accumulate soluble sugar which increases osmotic pressure in the
cell walls and enables them to withstand wilting.
• Increases DNA metabolism - Huvega increases the activity of several enzymes including those involved with
metabolizing RNA and DNA.
• Promotes high crop yields - Treating seeds with low concentrates of Huvega before sowing, improves their
rate of growth, development of roots and shoots and increases crop yield.
Whereas the product label only says "may be beneficial when used as a seedling solution, can be used in conjunction with chemical or organic nutrient solutions, ideal for use with leafy plants, vegetables and fruits". In the case of Botanicare, it is almost as if they actually over-simplify the purpose or mechanism of [some of] their products on the label.
The Calplex product appears to be simply calcium carbonate, not overpriced in my opinion and they don't try to glorify it as being anything more.
http://www.americanagritech.com/sites/default/files/brochures/OrganicareBrochure_1.pdf