Does an ambient light-rejecting screen really help in a lit room?

Yes, within limits. It rejects light arriving from the sides and above, so blacks stay darker and colors hold up with lamps on. It cannot fix direct light hitting the screen face or a very bright room.

Where should viewers sit relative to the screen?

ALR surfaces are directional. Keep seats within roughly the central cone in front of the screen; viewers far to the left or right see a dimmer, washed-out image.

Will it work with an ultra-short-throw projector?

Only if the screen is specified for UST. UST projectors need a surface with the right optical structure and a precise setup angle; a standard ALR screen will show hot spots and uneven brightness.

Do I need to mount it on a wall?

No. The stand holds the screen upright on the floor, so no drilling is needed. Check that the floor area in front of your seating can spare the footprint.

How do I keep the surface clean?

Dust it gently with a soft dry cloth and avoid abrasive cleaners or pressing hard on the material. Creases and ripples are hard to remove once the surface is stretched out of shape.

Is it better than a white screen?

In a room with light, yes for contrast. In a fully dark room, a good matte-white or high-gain screen gives a brighter, more even image across wider seating.