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From what I can see in the photo, it looks like a plastic simulation. I'm no coral expert but nature is not as symetrical as what you're holding. Maybe some of our coral experts will pop in.
Im not FW person but I would say it would not be as effective as CC or argonite sand. The reason is less surface area for the water to be in contact with. You get the buffering from the calcium carboniate the corals lay down as they build their skeliton. As the water disolves this calcium carbonite it increases the PH of the water. The greater surface area you have in contact with the water the greater the PH buffering ability.
No, it won't buffer your water much, as stated above. That bag you get will last your quite some time, but you will need to replace the CC from time to time - I do so about every 3-4 months for what I keep in my filter, so you will use it.