What it boils down to is these are the facts as far as the most current science is concerned.
1. The nitrifying bacteria that end up in tanks have been identified, re-identified , confirmed and reconfirmed.
2. These bacteria do not forms spores. So any bacterial starter that contains spores does not contain the right bacteria.
3. There are several strains of bacteria that convert ammonia to nitrite that are found in tanks. The ones in salt water and freshwater are different strains. So any starter product which states it works in salt and freshwater cannot contain the right bacteria.
4. Because of patents which are jointly held by Dr. Hovanec and the parent Company of Tetra, only their products can contain Nitrospira. Their products are Dr. Tim's One and Only (which comes in a salt and a fresh water variety) and SafeStart Plus which is a FW product. Any other product which contains live bacteria will contain Nitrobacter as a substitute for Nitrospira. This must replace the Nitrobacter for the cycle to be complete.
5. The bacteria live on hard surfaces all over a tank especially the top 1/2 inch or so of one's substrate. One can use filter squeezings or media as well as some substrate to seed a tank. This is less precise than using the battled bacteria because you cannot know how much bacteria is being added. However, it will definitely jump start a fishless cycle and reduce the time it takes to have a tank fully cycled. It is also less expensive than buying one o the two products above.
6. And then there is Caveat Emptor. Every maker claims their product works. However, if you cannot determine exactly what is in a specific product, it is more than likely that is because it is not what will colonize one a tank is actually cycled. Hoe can one use a product when they have no clue what is in it? Use some common sense,
7. The proof is in the pudding. The purpose of seeding bacteria in some form is to accelerate the cycle. How long any cycle might take is determined by how much of the two needed bacteria one has in a tank when they start to cycle it. Remember we are trying to get whatever is there when we start to double, the double again etc. until there are enough numbers that they can hold both ammonia and nitrite at undetectable levels.
8. The average fishless cycle where there are no live plants and no active seeding of bacteria takes 5-6 weeks. If one has actually jump started the process using the desired bacteria, that time will be shortened noticeably.
Given the proper sized bottle Dr. Tim's and some ammonia I can make any tank fully cycled and fully stocked in under a week and it only requires a single sddition of the product to do this. I defy readers here to do the same with any of the other products we have under discussion. The key factor here is not the presence of the ammonia oxidizers, rather it is the Nitrite oxidizers that matter. In a normal unaided cycle the bacteria colonize one after the other so first we see ammonia build up and then we have nitrite building up. Using the proper bacteria in a jump start means that, whatever amount of nitrite the ammonia bacteria present can create, there will be a commensurate number of nitrite bacteria present immediately to convert it to nitrate.
The hall marks of setting up a well planted tank, seeding bacteria from an established tank or using Dr. Tim's or SafeStart is that you should see little or no nitrite. In the well planted tank, especially a high light co2 added one, you may not ever see nitrate either.