Yes they are legal in all places open for mineral entry except anyplace designated as "Hands and Pans" only. Places like Bridgeport and parts of the Yuba River Parkway are hands and pans only and they mean it. Small hand suction dredges are very popular and sold in places like Placerville Hardware and other mining shops. I love mine.
According to local BLM if it doesn't have a gas motor on it, it's good. Electric motors with battery power to run them on things like trommels and pumps are fine, having a generator with a gas motor to run those electronics is not. You could totally hook a hand pump to a sluice if you want to in places that are not Hands and Pans only.