I used the citrus juicer yesterday.
I think it took longer, but it got more juice.
With the manual press, I'd spend about 5 seconds per lime half. I got whatever it extracted, then would throw away the piece.
With the citrus juicer, I spend 12 - 25 seconds per lime half.
It's also nice to have the graduated cup for the citrus juicer, so I can see how much juice it's produced.
The Black and Decker juicer is also interesting, because it rotates both clockwise and counter-clockwise. I don't know what determines which way it goes, but maybe they designed it like that so the motor wouldn't overheat in one direction?
Or maybe it serves a function and helps to extract juice, by being able to rotate both ways.