Apart from your lawnmower, the trimmer or edger may be the tool you use most. Very few lawnmowers will get everything, since most lawns butt up against a wall, patio bricks or have trees in the lawn. As a result, the only way to keep that lawn looking really neat is to finish the job with an edger of some kind.
But which kind?
Traditional edgers are dual blade affairs with a long wooden handle. Despite the aging design, they still do the job and do it well. They require no gasoline, are lightweight and there's no cord to get in the way. If the blades are kept clean and sharp, they can edge a 20 ft x 40 ft patio or 30 feet of sidewalk in a few minutes.
But they do require a lot of muscular effort. For those who still enjoy working outside, but may be getting along in years, they may not be practical. It's no fun to keep a yard looking trim when the result is an aching back and sore wrists.
A step up is an electric trimmer. Inexpensive and easy to use, they remove shaggy grass by slicing it off with a rapidly whirling plastic string. The cartridge holding the string is easy to replace, lasts for several weeks to months and costs only a few dollars to replenish.
They have another advantage over manual trimmers: they can easily be worked at different angles and in areas that manual edgers can't work. If you have a lawn that abuts against an outbuilding, such as a shed, it can be very difficult to use a pole trimmer to remove the grass. An electric works great.
Ditto, if you have grass that winds around large rocks or a lawn that is bordered by scallop-shaped bricks, using a manual pole edger is out of the question. But the string style edger works perfectly in these circumstances. It does no damage to the bricks and removes grass easily.
A step up in some eyes, a difficulty in others, yet another style of power edger uses a small gasoline-powered motor. They're a bit noisy, but the largest drawback may be the weight. They're much heavier than electric trimmers. On the other hand, they have no cord to get in the way.
Since there's no cord, they also have no restrictions on where you can take them. If you have a large yard, or want to trim in certain areas where there's no outlet nearby, using an electric trimmer can be near impossible. Using a couple of hundred feet of extension cord makes the job unpleasant, and the cord itself is heavy at that length. In those circumstances, a gasoline powered trimmer can work wonders.
Gasoline-powered edgers also typically have much more power. So if you have thick brush, weeds or other debris that you want whacked down to size, this type can do the job. They do cost a bit more, but they last for years and the investment is worthwhile for the effort they save.