I was just about to buy some compressed air to clear my Power Mac's innards and noticed that some brands are more expensive than others (e.g. Kensington costs more than Office Max brand). Are all brands the same? Is it just air in there or what? I know it's an anal question, but hey - I'm a Mac user! (Plus my Mac is probably the most expensive thing I own after my car and I will go to great lengths takes to protect it). Thanks.