Most of the dats promising to make your ! bigger are just plain scams. They promise amazing results but simply don't deliver. The companies that produce them rely on the fact that even if you are dissatisfied, you would never return them - because you'd essentially be saying that your ! was small, and it remains so.
Even worse, the dats are not regulated by the FDA, and while most just contain a mix of vitamins and minerals, there's no real way to tell what all is in them and how it will react with your system.
Generally speaking, the !s you already have are probably good enough. Try talking with the people you play with and get a good feeling for what they think about it, and I am sure you can find a way to make your ! more than adequate for everyone.