I have a metro data/vac 3 and am very happy with it I do pc and printer service and I get good suction you need to change your bags when you notice it not cleaning well. There dead silent in an office environment and the adapter to use it as a blower is in the kit so it’s basically the same as the $70 metro vac blower and you can clean toner up with it.
As far as air compressors go I use them all the time never had a problem with moisture. In reality you never should unless you can see water vapor coming from your blow gun at what point you should drain your compressors tank as the manual tells you to do daily. I have a Porter-Cable model c1010 and there good cheap, oil-less, and quite throw a coil hose and blow gun and you have a complete solution for blowing out computers
An option I haven’t got to try but really am excited about is Power Tank Sidearm system it’s basically a co2 tank for paint ball with a regulator and hose a bit pricy but it would last longer and deliver high pressure longer than caned air. I am sure you could build the same system for way less in components then there charging for it.
Metro Vacuum MDV3TCA DataVac/3
PORTER-CABLE C1010
http://www.amazon.com/PORTER-CABLE-C1010-Heavy-Duty-1-Gallon-Compressor/dp/B00519EUCE
Power Tank PS01-3150 Sidearm Package B