I've tried digestive bitters. They did little or nothing for me. If anything, nowadays, I avoid spicey food and that would follow for drinks too. I put it down as one of those "great ideas" that may help folk with acute, as opposed to chronic, health conditions.
Fat digestion is pretty tricky with me/cfs in my experience. Too little and you stop making hormones and your lymph can't move. Too much and you're over-grounded and constipated. I can't process the fat in meat, apart from lamb liver, so that's the one i eat. Ghee, i can tolerate every other day and amaranth (for the other day) has a fair bit of oil in it. So i eat fat once a day, either ghee or amaranth.
For me I can move forward on that as it allows me to repair the leaky gut. In a chronically ill situation, i don't think bitters will help much and may hinder; being just more stuff for an already compromised body to process. Less is more (most of the time) imo.