I'm not a poop addict, I definately agree that trace elements are necessary, I actually use micro calmag and overdrive in my organic regiment, making it not fully organic. But using ro water, I found it's necessary.
My sister lives in a really heavy sulfur well water area, sucks, smells like rotten eggs. I'm lucky to have just moved in an area with great water, 100-110 ppm. I still plan on using the ro though.
I've never said anything bad about Gravity, actually saw an increase in yield, but it didn't smoke as good. It was a huge garden, and might have had a little to do with not being able to tend to all of the plants as well as it could have been done, 25#s is a shitload of work.
Good luck with the Gravity, but be careful with it, dilute the hell out of it.