I have 120lbs of the Hirocks stuff. It's not bad, but extremely heavy and not that porous. I did get some very big pieces though and I like that - Big is good for the bottom pieces.
I put 4 big pieces in my 215 a few weeks ago and they are already starting to blend in. One problem I had is that in addition to being heavy, they are very, very hard. I drilled into them to insert acrylic rods (as feet) and basically ruined a few masonry bits. I don't know what this stuff is, but it's harder than cement. I was able to drill through the live rock like it was styrofoam.
Art