If you use the lowest mix rate, and avoid applying during the hottest months (June - Oct here), you can see good results. Maybe it’s just my yard, but the St. Augustine is never really happy for about a month after I’ve put it down.
I was actually a little disappointed in the performance of the product. We had moved into a new home in November and the builder had sodded the property with Bahia that was full of weeds, including thistle and dollar weed which had spread. After spraying according to the heaviest concentration shown on the label, the thistle was barely dented although it did seem to do a relatively good job on the dollar weed and some of the other weeds I couldn't identify.