Does an edger save time or keep edges in tact longer than using a trimmer upside down? I notice that they always make the dirt be more visable somehow. One thing I notice is that it's sometimes hard to go fast with a trimmer and get really straight work. Is an edger quicker? How often must u do this? I can make pretty nice edges the way I'm doing it now so why get put out more $ for something else like that?