Due to the low solubility of the glyphosate in water the more soluble salts of the parent acid are used for herbicidal purposes. The most widely used glyphosate based hericide is Roundup Ultra. This particular product is used on an international basis and more of it is sold than any other competing herbicide. This product is marketed by the Monsato Company. Roundup Ultra supplies glyphosate in the form of it's isopropylamine salt. Recently, however, Zeneca have released their own glyphosate-based herbicide called Touchdown which is the trimethylsulfonium salt of the parent acid.(The structures of these two salts are shown below.)

Both off these products contain the same active ingredient, the glyphosate anion, and as a result there is no difference in their biological activity because once inside the plant the counter-ion dissociates. Only the glyphosate anion bonds to the active site in the enzyme and so a counter-ion can have no effect.

It is possible, however, that the counter-ion affects the rate of absorption in to the plant. Zeneca claim that their product is absorbed more quickly, but i can find no evidence to substantiate or debunk their claim. In reality there is no further differences between these two products except for trivialities like their concentrations and whether they contain surfactants or not.