The lava rock I got is very light and very porous. I would even say lighter than the Fiji I used to have in my reef. Not a lot of the holes that go through the rock, but when stacked, there are multiple caves and places to hide and/or swim through. Never have had issues with circulation.
I'm not saying my way is the best for everyone. For a reef tank, I would go with more traditional Fiji, Tonga, etc. I like the "plainness" of the black lava rock for my FOWLR
though. To me, a reef is about everything inside the tank. I've always liked my FOWLRs to focus more on the fish.