We have done it but I've posted all over about it so I'm guessing you are looking for some other perspectives

We've done a lot of supplements because we worked with a DAN doctor, her perspective was that the omega 3 chewables were not a high enough dosage for a child with neuro issues and we needed to do the cod liver oil, we just mix it in juice and since they rarely get juice otherwise they happily drink it. We also did B-12 nasal spray and glutathione cream which helped a lot but are prohibitively expensive for me right now. Probiotics are really important also. Right now I am doing fermented foods which is a wonderful source of probiotics too but a whole 'nother topic. Mineral supplements are often needed (calcium and zinc especially) to help picky eaters notice taste over texture and get on track with healthier foods.

GFCF is the single most helpful thing we've ever done for our daughter's SPD, by a long shot - my experience is it is at least 10 times more effective than OT. I really really did not think it would work, I thought I was doing it just to rule it out so I could say I tried it and get the doctor to move on to other ideas. When we started GFCF we also did a supplement called intestimend from brain child nutritionals, it was expensive but it accelerated her gut healing and I think it is in part responsible for the fact that she reacts to fewer foods now than she used to.