There is scientific evidence on these "cycling" products. There is, so far, only one product that does instantly cycle, and that is
Dr. Tim's One and Only. I have never used it because I have never "cycled" an aquarium, I have plants and that avoids any and all cycling as a necessity.
Dr. Tim Hovanec led a team of scientists that researched into the cycling issue. Below are excerpts from my article on bacteria that is on
@AbbeysDad blog if anyone wants further details, but I will mention that the article needs revision with respect to the role of archaea and I haven't yet got to it..
https://mjvaquatics.com/bacteria-in-the-freshwater-aquarium/
Nitrification is the oxidation of ammonia/ammonium to nitrite and then the subsequent oxidation of nitrite to nitrate; this is performed by two groups of bacteria known collectively as nitrifying bacteria or nitrifiers. True nitrifying bacteria are autotrophs; they use chemosynthesis to manufacture their energy by using oxygen plus nitrogenous waste (ammonia or nitrite) and carbon (from CO2). There are several different bacterium species involved, all in the family Nitrobacteraceae, that carry out this function in soil, and it used to be thought that these, particularly Nitrosomonas europa and Nitrobacter, were the nitrification bacteria in freshwater. But Dr. Timothy Hovanec led the team of scientists that proved this to be a mistaken assumption. Ammonia is converted to nitrite by bacteria of the Nitrosonomas marina-like strain [2] and nitrite is converted to nitrate by bacteria closely related to Nitrospira moscoviensis and Nitrospira marina. [3] With several subsequent scientific studies by other scientists on wastewater nitrifying bacteria this data is now accepted.
[2] Paul C. Burrell, Carol M. Phalen, and Timothy A. Hovanec, “Identification of Bacteria Responsible for Ammonia Oxidation in Freshwater Aquaria,” Applied and Environmental Microbiology, December 2001, pp. 5791-5800.
[3] Hovanec, T. A., L. T. Taylor, A. Blakis and E. F. DeLong (1998), “Nitrospira- Like Bacteria Associated with Nitrite Oxidation in Freshwater Aquaria,” Applied and Environmental Microbiology, Vol. 64, No. 1, pp. 258-264.
Dr. Tim's One and Only is so far as I have seen the only product containing the required bacteria and the claim that if the directions are followed the aquarium is cycled has never been disproven. Dr. Hovanec also carried out studies on several products including API's Quick Start. His determined that none of these contain the specific bacteria strains that do the nitrification, but he admitted that his tests showed some (like the API) do speed up the cycling process. Cycling normally takes anywhere from two to eight weeks (under suitable conditions) and the use of the Qjuick Start sped up the cycling by a couple of days. He reasoned that even though the actual strains of bacteria in this product were not nitrifiers, the bacteria did somehow "improve" conditions for the establishment of the nitrifiers. You can find information and (I believe) the scientific papers on Dr. Hovanec's website:
Yes, there really is a Dr. Tim. Dr. Hovanec earned his Ph.D. in Ecology, Evolution and Marine Biology at the University of California, Santa Barbara, where he investigated the phylogenetics of nitrifying bacteria in aquaria and Mono Lake, California. Dr. Hovanec was the first to demonstrate that...
www.drtimsaquatics.com