I have not seen Ginger Bitters in a while. The only drawback to ginger is that it is an antacid. So this would not be by first choice. Someone posted about Chinese Bitters, which looked really good and Floradix makes a good bitters.
I like to take them right before I eat, but they can be taken during or after. It really does not matter. And you only need a very small amount, enough to taste it. So I recommend a half dropper full on the tongue around meals.
Remember to drink plenty of water throughout the day when using bitters due to the liver detoxification.