A Bazooka is basically like a suction nozzle. It has jets near the nose which push the water back through the tube. A collection tray is near the discharge end of the tube which collects the gold.
Some people say they lose gold, some people say they don't- I've never used one. But one thing is for sure, a dredge has a much larger area of sluice box for recovery. Bazooka's are more portable.