It times a sound pulse rather than light. The important consequence is that sound leaves as a widening cone rather than a narrow spot, so the reading comes from whatever is closest anywhere in that cone. A laser measures to a specific point; an ultrasonic meter measures to an area.

No, and this is the most common misunderstanding. The pointer only indicates roughly where the unit is aimed; the measurement is made entirely by the ultrasonic pulse and its cone. A reading can legitimately come from an object well away from the visible dot.

Typically quoted as a percentage of the measured distance rather than a fixed tolerance, so absolute error grows with range. Air temperature also affects the speed of sound and therefore the reading. They are suited to approximate work rather than to anything with a dimensional tolerance.

Broad, flat and roughly perpendicular, to return a usable echo. Angled surfaces deflect the pulse away, and soft or heavily textured surfaces absorb it. Cluttered spaces are the real problem, since anything intruding into the cone is measured in preference to the intended target.

Where cost matters and precision does not - rough room sizing for estimating, stock-taking, or a quick check of a clear span. For any dimensional work, setting out, or measurement that will be quoted or built to, a laser distance meter is the correct instrument.

Because different objects fall inside the measuring cone as the unit is moved slightly, and each becomes the nearest reflector in turn. The meter reports each as a valid reading with no warning. Moving to a clear line of sight, or switching to a laser meter, is the only reliable answer.

Temperature does, because it changes the speed of sound and therefore the calculated distance; better units compensate for it automatically. Humidity has a much smaller effect. Neither matters for the approximate work these meters suit, but both rule them out where a stated tolerance is needed.