My take, from personal experience and after being involved probably 100+ "help me cycle my tank" threads here on R2R:
Only Fritz Turbostart 900 works to mitigate ammonia in a very short period of time. In as little as 24-48 hours, Turbostart can make a new tank (dry rock and sand) tank safe for fish. My understanding is that this product contains one or more heterotrophic bacteria that are not true nitrifiers, but they can handle the ammonia while the true nitrifiers populate.
Turbostart is now the only bacteria product I suggest using to cycle a new tank, and, much more importantly, I know that Randy Holmes-Farley recommends the same product:
https://www.reef2reef.com/threads/p...-time-big-water-change.1115070/#post-13638874
All other bacteria-in-a-bottle products seem to take +/- 3 weeks to establish a viable biofilter that would make. it safe to add fish. This includes Dr. Tim's One and Only, Brightwell's Microbacter, Seachem's Stability and others.
If you added no bacteria products at all, your tank would cycle on its own in about 3 weeks. Therefore, I don't see a need to add any of these products anymore, though they may have some small benefits to the cycle. I've used these products myself over the years, and I'm not going to go so far as to call them "snake oil", but I am now doubting if you really need them.
I'll add, Dr. Tim seems to have gotten himself in some legal hot water, and I'm not saying at all that he's guilty, but until this gets resolved I'm hesitant to suggest any of his products:
https://www.reef2reef.com/threads/alleged-issues-effecting-dr-tims.1157751/
This is yet another good thread taking a hard look at these bacteria-in-a-bottle products:
https://www.reef2reef.com/threads/n...-equal-whos-who-and-what-do-they-need.989780/
I hope this helps!