I've never read anything negative about artificially colored rock and I've looked at it with admiration myself. I have always put it back in the bin because I would rather start with a grey or white rock and then I can monitor coraline algae and other growth a little easier than on a purple tinted base.
I presume that the growth surfaces on the two rocks are comparible, but again I trust natural rock more than artificial. I have no proof natural is better or superior, or not. I think if you like how it looks it should work out fine for you in the long run.
I trust other folk with more specific knowledge may chime in? This is a good topic/question that I have wondered about myself.
Thanks for asking
Kris
Edit: Oh, and 1 pound per gallon is an old "guideline" that was based upon selling rock instead of science. There is no magic number. I put most of my rock in the sump but have way less than 1 lb per gallon. The surface area and bacteria on/in the rock are what we need for filtering, and you need some number based upon what else you put in the tank. GL