Long story short, the only "bacteria in a bottle" product that has been proven to work was Bio-Spira, however, it is no longer available for freshwater, only for marine tanks. Tetra Safe start is a product similar in theory to Bio-Spira except that it does not need to be refrigerated, however, you should know that it is still temperature sensitive, at any point from the manufacturer to your door if the product got too hot or too cold the bacteria would have died and it won't work. That being said, it won't hurt anything to use it. Since you have already purchased it, go a head and use it if you want to, or you can return it. Some people have had great success with it while for others it did not do a thing. The bottom line is it MIGHT work, if, and only if, all temperature precautions were taken through out its shipment process from the manufacturer to you door. If you do choose to use it, and you do not use the entire bottle, it is advised that you keep the open bottle in the fridge to get the longest possible shelf life. You also want to shake the bottle up well before use as the bacteria tend to settle at the bottom of the bottle. You may be lucky and be in the group that it works for, but don't expect miracles ... it most certainly will NOT (despite its claims) cycle you tank overnight.
Edit: As an additional note, I have tried two products similar to Bio-Spira, Dr. Tims One and Only, and most recently Tetra Safe Start. I have a 10 gallon tank with a small sponge filter I was trying to cycle for use in a QT tank (I have since moved the sponge filter to an established tank where it will stay until it is needed). At any rate, as I had no luck with Dr. Tims I thought I would try Tetra Safe Start, again I had no luck. You can use either of these products with a fish less cycle, however, you need to vary your approach. If you use either of these with a fish less cycle you need to only dose your tank to 2ppm initially, then slowly (very slowly) increase to 4ppm. Again neither of the products hurt my cycle, but neither sped them up. There is another product, called Nite-Out II, I have not used the product my self, but there was a member on this forum that was having an extremely difficult time with her cycle, and she used the product and it worked, she did not follow the directions exactly, you are suppose to dose the tank several times over a period of 2 weeks with Nite-Out, but she just dumped the entire bottle in the tank. Not sure if this was an isolated case or if the product actually works. But as for Tetra Safe Start, it did not work for me, but it didn't hurt anything either.
