Does anyone use an electric vacuum pump?

Does anyone use an electric vacuum pump to provide vacuum to the power booster? How well do they work? I heard it takes to long for them to rebuild the vacuum after coming to a stop. I ask because i have a 440 in my dart with a mopar purple shaft cam. it wont provide enough vacuum for the booster. I bought and installed an aftermarket 8" dual diaphram booster. its small because the original booster wouldnt fit with the 440. The manufacturer says it wont work without at least 18 inches of vacuum.