Both DrTims One and Only and Tetra's SafeStart both contain the proper bacteria for the rapid cycling of a new tank. However, if the product is mishandled before one gets it, that is allowing it to freeze or get over 95-100F, it will likely not work well if at all as these temps can kill the bacteria. Also Dr tims contains a date packaged (not sure on the Tetra). Ideally it sould be used within 6 months of the date and never if a year over. At the older age it will still work but much much more slowly. This can be somewhat mitigated by storing it about 50F.
Now folks who fail to follow the directions properly and then don't get the results promised usually resort to claiming the product doesn't work. Dr Tims sure worked fine for me twice now. Well I cheated. I dosed 1/2 the amount and finished up with ammonia dosing. But I didn't need an almost instant cycle I needed a jump start free of any other bacteria that would result from seeding from another tank. I used the half dose as it allowed me to do this twice for the price of once.
There are a number a large public aquariums who have used the sw product to get tanks of up to 1,000,000 gallons cycled fast. So ask yourself, would you fill a million gallon sw tank with inhabitants if you had not thoroughly investigated whether the cycling product worked or not? Would you even have bought it if you did not have adequate evidence that it worked?