I highly recommend you to read the article throughly before ask more questions. The answers to your questions are all in there.
Tetra SafeStart is proven working. It has the correct species of bacteria required to jump start your aquarium nitrogen cycle. I have used it on multiple occasions to jump start the cycling in several of my new aquariums. It has always worked. It is not just me. We have done a survey on another forum a while ago, majority of the (hundreds) people who had tried it all claim it had worked for them. With Tetra SafeStart, it will cut down your cycling time considerably.
You need to be careful with some other live bacteria products. Many others are not having the correct species of bacteria.