I also use it when I know I have to eat out, especially for work-related functions where I don't know what will be served or how it will be prepared. (I keep a meal replacement bar in my purse for those occasions in case the food has no good options and will eat that instead.
I have a sensitive stomach too, but have been ok with the F&C Blocker. I just drink lots of water when I take it. I find it to be a bit binding, but have been ok when I do Greek Yogurt for breakfast the next day to get some good probiotics in me.