It's the only legitimate bacterial catalyst being sold. I have used it and it works awesome. Your tank will be cycled in 2-5 days after adding it. I've have only heard positive responses from people who have used BioSpira®. Froggyfox says it doesn't always work - well, that could be true if it is not promptly refrigerated after transport (it comes packed with dry ice when shipped directly to distributors). If the distributor were to neglect a box of BioSpira® and allow the dry ice to evaporate - then sure - it wouldn't be long before the bacteria would come out of stasis and starve. Also, if the LFS carrying it lost power for a day or so that could affect the efficacy of BioSpira®. All in all I'd guess that wouldn't be likely though.