Dry chemical extinguishers also attack aluminum. That is why you will no find then in aircraft or in aircraft hangers.
While a powder extinguisher works great at extinguishing fires (and these balls are full of that kind of powder), be warned that you can pretty much throw away all the electronics in the room after one has been used, including your printer. Powder extinguishers are no longer allowed in most public buildings in the Netherlands for that reason because they cause so much residual damage, as well as being a powerful laxative for people exposed to the powder. Insurance companies are behind prohibiting their use, and you are sometimes not covered if you use a powder extinguisher. I've seen expensive cars totaled because of the use of a powder extinguisher - put out the fire, but replacing the wiring harness and all the electronics meant that the car was declared totaled.
