I don't know, really. My Sweet boy always had terrible hair ball problems too, that got much worse as he got older.
I think part of the issue for Struvite Kitty is, in part, the years on the c/d kibble, but it started even before that. She'd been with me just about a year, and she started this awful projectile vomiting. It was the weekend of course and I took her to the on call vet, they did an x ray and all we could see was a lump that was, at the time of x ray, leaving her stomach and entering the intestines, and a massive amount of gas. I've teased her for years about her $400 hairball, LOL. Vet felt pretty sure the mass was a hairball, and prescribed large doses of hair ball remedy until she passed it. Since then, she has always needed help. After loosing my Sweet Pea, who also took massive doses of the stuff, to the cancer, I became determined to get all cats off ALL petroleum products. I actually started that process before he died, with the coconut oil.
So SK is OFF all petroleum hair ball remedies. She's still getting the Vets'-Best as garnish for her small meat chunks, but I'm hoping that, by the time she no longer needs the V-B to eat the raw chunks, the egg yolk lecithin will have solved her problem.
Little Cat may not need any help now that she is almost completely raw. Top Cat will continue with the pumpkin. It is harmless, she likes it, and it works for her.
Incidentally, SK STILL needs a pepcid every five or six days. I don't know why. But every five or six days, she gets some acid reflux and either vomits or regurgitates. If I don't give her a pepcid on the day she does it, she continues to do it until I do. Maybe the egg yolk lecithin will help with that too, if it is, as I suspect, hairball related.