Be careful with long lines if you have a dog. They can get tangled up in the long line quite easily. If you go this route and have a dog, make your droppers long enough that the dog can swim over the main line.
Also, they're not really that much faster than setting the decoys individually. You can spool the line and attach the decoys as you set the long line. If you kept the decoys attached you'll really have to watch for tangles etc. Longlines work best in deep water where you don't want to mess with lines 20 feet or longer on each decoy.