Tetra, like so many other companies/shops, do not believe in fishless cycling. After all, they want to sell you their product and unless you think that it will make it safe for fish instantly, you won't buy it. If you stock the tank very slowly, a few fish at a time, you might get away with it - if the Safe Start is in good condition. The only way to prove it is to add ammonia to substitute for fish and see if the tank can clear a 3 ppm dose in 24 hours.
Do you intend having live plants from the start? If you do, it makes it easier as plants use the ammonia made by the fish as fertiliser. But you do have to make sure the plants are doing well before getting fish as the last thing you want is to get plants, get fish and then find the plants have died. And with this method, you will need to get just a few fish at first and add more a few at a time over a dew weeks, testing regularly to make sure that no ammonia or nitrite shows up. If you do this method, you should add Safe Start when yuo get the fist small batch of fish.
You will need to do a water change of about 50% every week. If you don't have live plants, or you have only a few, you need to clean the gravel at the same time, avoiding the roots of any plants you have. This is one advantage of sand, you can see where the muck is as it sits on top of the sand. The downside is that the muck sits on top of the sand and you can see it