Line lasers come with various mounts, casings and other ways to keep them steady and level. Some will alert you with different colors or beeping noises if you've placed them outside of the designated level. Finding the right style for your job and personal liking can make using the line laser simpler and save you time.
Line or Dot ?
Line lasers offer more versatility as they require less manuvering to transfer levels.
However, a dot laser will give you considerably more range due to the increase in brightness of a concentrated laser dot. If you can't decide which would be more functional, consider buying a combination unit that offers both.