Haven't used it yet.
I use this primarily in ciders for post MLF adjustments where malic and/or citric additions would be inappropriate. Since I also keep malic acid on hand for cider must adjustments and citric for cooking, I also use this to make my own three acid blends for fruit wines.
I use it to lower the pH of fermenting must so it doesn't spoil, and acts as a preservative when its done. It also adds some tartness. Easy to use.