I have one of those $20 Harbor Fright lasers and it is a toy. You still need
another level to set up the straight line feature (the clip on) and if you
don't shoot it absolutely level from laser to the wall it will "belly".
The beam is too weak to use outside.
If you are just putting up pictures or shelves it can work but not any better
than a yardstick and some string.
If you are laying out a foundation or grading your yard use a hose and water.