This reminds me of a backpacking saying.
"If you think ounces, the pounds shave off"
So- do you have any plans to go with lightweight stuff on other parts of your rig? If not, I would go steel. But if you are always trying to shave off weight, then it might be a good way to do it.
IMO- the steel one is going to take a hit a lot better, but the aluminum looks cooler.