because those are the 2 that UB has recommended through out the years, I have had great results with both.Dynagro and jack's classic are totally different types of products. Jack's classic is meant for soil and potting mixes, while dynagro is a complete hydroponic formula.
Yes, they are both popular with the same group, but that doesn't mean they are interchangeable. I can't understand why Jack's classic is always mentioned when DG is.