I'm reading that many of these artificial rocks are like dense cement blocks. I want to be environmentally sensitive but not sure the compromise is worthwhile. Is there a real reef rock that Has a minimal impact on the environment?
Nah.
Sure there may be no unwanted pests and it may not need cleaning or curing, but your missing out on all the exotic goodies from the ocean too.
Sometimes unwanted pests may even be something you never knew you actually wanted, like it was with me and my first Mantis Shrimp.