My tank has some rust and someone has already Kreemed it once, does this stuff really work or should i just look for a good tank.

 

Done right, it works fine. In order to do it right again you will need to remove all existing rust inside the tank. Sounds like this was not done the last time. This has been covered to some extent before with adding media to the inside of the tank like small nuts , stones, coarse sand or whatever and use some method to rotate the tank slowly. This may take overnight to happen. If not 100% bare metal inside, any treatment will be a failure in short order. One word of advice, as ethenol is becoming more popular choose a coating that is ethenol resistant and future problems won't exist.
Ron