I use a very wide range of organic fertilizers of all sorts. There is no way to tell what did what in my yard. Sul-po-mag, potassium sulfate, bone meal, Mighty Grow, greensand, azomite, crab meal, raw milk, aerated worm tea, mulch, cover crops, mycorrhizae inoculants, hugs and kisses, urine........
I didn't have any negative effects shortly after use. It seemed like a quality product. I think they use a better process than the cheaper fish I picked up from the wholesaler. I researched it a while back but I can't remember the specifics.