Entirely agree, especially with the trial and error. I have migraines, and I've never been able to persist with a trigger diary or app, which is pretty much similar. To make it really work, you need to capture too much data about both the food/beverage intake and symptoms, and even then, you need to move on to trial and error to confirm the statistical results. As annoying as it is and how much time it takes, I found an elimination diet much easier: you start with a handful of whatever foods/drinks you find "safe", and add new foods/drinks one at a time, with at least a couple of days in between each new item.

The virtue of using the FODMAP pattern for me -- aside from determining whether the problem really was FODMAPs -- is that the food pattern came pre-clustered. If you don't cluster somehow but instead do foods entirely one at a time, an elimination diet goes on forever. However, you can create your own clusters to add back in. Start with a week eating only the foods/drinks that you know are "safe", ignoring everything else you care about in your diet -- heck, you can do it with Ensure. Once your system has calmed down, then you can say, hypothetically: "On Monday I'm going to add back in foods with gluten. If I don't react by Thursday or Friday, I'm going to add back in cruciferous vegetables. If I do react by Thursday or Friday, I'm going to have smaller amounts of gluten foods, or just white toast, or whatever, until I nail the gluten food situation down. After that, I'll move on to cruciferous vegetables." (I invented those examples -- you get the drift.)

That way, it's just a day-to-day dialog between your GI tract and specific foods, not something you need to sort out statistically from weeks or months of a diary or an app. Because, ugh.