I found it surprisingly correct, especially given that I hadn't asked our chiro to do it, he just did when I went in with my son (2wks-ish at the time) for a follow-up visit for me. He's the one who first said that gluten, some dairy (plain milk not ok, but cultured/fermented like yogurt and cheese were ok) and chocolate were problematic. But it wasn't 100% accurate, here was our breakdown:
me: milk and chocolate bad, cheese/yogurt (fermented/cultured dairy) ok
daughter: gluten, milk and chocolate bad, cheese/yogurt ok
son: gluten, milk and chocolate bad, cheese/yogurt ok
me: gluten and all dairy bad (but gluten and fermented/cultured dairy seem to be mercury toxicity related, no gastro symptoms or any sort of normal bad reactions)
daughter: gluten and milk are bad, haven't seen chocolate be bad, cut out remaining dairy to keep the household the same but no concrete issues that I think were cheese/yogurt related so I think he was right on this one
son: gluten, all dairy, chocolate and cashews are bad (was surprised with the chocolate, that caused a face rash that I didn't notice until more than a year later because he wasn't getting a lot of chocolate)--and, he has different reactions to real milk (vomiting) vs cheese/yogurt (mercury-toxicity related, no gastro/rash/normal problems)--and I don't think our chiro checked any nuts, I think he was just testing his basic most-likelies list
So to me, it seemed like he was more accurate than guessing should've produced, but somehow I think he was almost asking the wrong questions for the gluten/cheese type foods for our situation. Based on our experience with it, I'd say it's worth a good try.
One thing to consider (not sure if you already have) is food chemicals, things like salicylates and amines and phenols and such. Diets like Failsafe and Feingold address some of these, I think. I'd think the your ND would have to be familiar with these in order to ask correctly.
There's also a link somewhere to a video someone made on how to use a crystal to basically do this on your own. Several people have had great success with that. Since our list is short and well-defined at this point, I haven't done it myself.