Personally I think that the chances of dust getting inside a rocket blower are pretty remeote. It's certainly not something that I'd worry too much about.
It shouldn't suck dust in as there's a filter on the end the air goes in and on the end the air comes out there's a valve to prevent backblow.
This is the whole point of buying a blower designed for cleaning out cameras and other stuff.
Here it is...
http://www.giottos.com/Rocket-air.htm
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