I've used zeo for about a year now. Curiousity got the better of me.
As far as husbandry goes, I'm extremely diligent, down to small, automated daily waterchanges. I wanted to see if I could improve things in terms of color and polyp extension. I was rather pessimistic getting started. After about 6 months, I was beginning to think that I could probably achieve the same results if I stopped the zeo dosing and removed the reactor from my system. I went without zeo for another 2 months.
After the 2 months, I thought I should probably use up the rest of my zeo supplies, so I put the reactor back online, and began dosing again. I noticed an immediate improvement and a big growth spurt.
There's so many factors to reefkeeping, it's impossible for me to say that the zeo caused that effect, but the bottom line is that to me, it appears to make a difference in my system, and I'll continue to use it. As Jackson6745 mentioned, a low nutrient tank can be achieved through other means, so IMO, zeovit is definately not necessary to have colorful healthy corals.
-E.