Environmentally friendly my rear! Taking a 2.5 lb brick of aluminum and machining it down to .25 lb is Incredibly wasteful. Not only do you have 2.25 lb of waste (that needs to be shipped back to a recycling plant to be remelted to another brick of aluminum), but machining a brick of aluminum takes a lot of time. In that time you require a lot of power to run the Mill, a lot of coolant (oil) to keep the drill bit cool, and a lot of NOT environmentally friendly cleansers to get the oil off of the finished part!
You can get the same part (or nearly so) by punching out a thin sheet of aluminum the desired thickness. The punch would not only give you the desired shape (with all mounting holes), but it would also reduce time, effort, and waste by a great deal.