A while back I wrote the rep for my region via email and they sent me a sample pack. I told them I wanted to run a side by side with H&G which is partially true. Anyway, I've run their entire line on an OG Kush clone that I took from a mother plant that was grown with H&G so while not side by side, a great basis for comparison. Pretty much equal conditions for both plants.
I am a Hydro/DWC grower and here are my thoughts, 39 days into flowering:
Definitely need to add a Cal/Mag Supplement;
Noticeable Salt Deposits when I changed my Res, Remedied with H&G Drip Clean;
The Base Nutes are Meh, Reminds me a lot of the CNS17 line by Botnicare;
Supplements are money, Supercharge & Resinator;
Plant loves the stuff, Roots are Pearly White...this was not exactly the case with the Mother.
Overall, I have been pretty pleased. The real questions will be answered at Harvest time, and I still have some weeks to go. The plant is shaping up to be a very nice producer by appearances at this stage.
I'd say Rock is definitely worth a try, especially if you work a free sample kit out of the deal.