These machines cut greenery with whirling plastic lines, can trim right up to trees, steps, and rocks. They're great for maintaining a neat edge along walks and beds, and they can tidy a rocky hillside that's too irregular to mow. Many can also accept a metal blade for leveling tough scrub and small saplings.
Gas Powered Models
PROS: Power to clean up a big yard, large cutting swath (16 to 18 inches)
CONS: Weight, noise, pollution, maintenance; the need to keep gas and oil on hand
PROS: Portability and light weight; low price ($50 to $150); less noise
CONS: Less power; limited extension-cord reach or battery life; small cutting swath (12 to 15 inches); can't handle brush cutting
Electric With Cord
While not able to saw brush, a 3-amp or better corded electric machine is powerful enough to clean up a suburban yard, provided you've got outdoor outlets and a long extension cord. Plus, it's the least expensive option.
Cordless trimmers can handle grass and weeds in a small yard, and they're easy to toss in the trunk when it's your turn to tidy Grandma's patio. The rechargeable 12-volt battery means no hassling with extension cords or gas-oil mixtures, and purchasing a spare battery pack will alleviate the disadvantage of the short run time.
Typically, trimmer string comes wound around the head and is slowly eaten away with use. Some heads release more string automatically; others you tap on the ground. Eventually, when the spool is empty, you have to stop and wind a new one.