They allow close trimming only on the opposite the bag. When shopping for a bagger, be sure to remove the bag from mower and replace it in order to evaluate the ease of the operation. Also check the size of the bag opening. A small opening clogs more easily and inhibits quick and easy dumping of the clippings. Manufactures use steel, aluminum polycarbonate or Xenoy resin for the deck material.
Steel costs less but rusts, shortening the life of the mower.
Aluminum is a little heavier, but does not rust. Decks of modern plastics are virtually indestructible. Finally, plastic catcher bags are generally more durable than cloth bags. Self-propelled rotary mowers use a power drive mechanism. These machines require the operator to squeeze a bar or a lever to engage the mower.