Without sitting on the fence, honestly, there isn't a direct comparison. Grass Trimmers are great at what they're made more which is trimming, whereas lawn mowers are great for their purpose and that’s mowing the lawn. If you're not a perfectionist and don't need perfect edges, a lawn mower will do a perfect job. But if you want that manicured professional-looking lawn, you're going to need a grass trimmer to get those edges. The combination of both will leave you with a neat and consistent lawn, with crisp edges and that picture perfect finish.