What can I see with an 80mm, 400mm refractor?

The Moon in good detail, Jupiter and its moons, Saturn's rings and bright objects like the Orion Nebula. Deep-sky targets appear as faint smudges rather than detailed structures.

Is 120X magnification realistic?

Rarely. An 80mm lens tops out around 160X in theory, but the short focal length and light mount make high power dim and shaky. Most viewing is best between 20X and 80X.

Does it come with eyepieces?

The listing does not specify eyepieces or a finder. Check the box contents before buying, since you may need to add an eyepiece and finder to use it comfortably.

Is it good for a child?

Yes for the Moon and daytime use, and the sticker sheets appeal to kids. An adult should set it up and help with aiming, since the mount is basic.

Can I use it for birdwatching or landscapes?

Yes. A refractor gives upright views for terrestrial use, though the image may be mirrored depending on the diagonal supplied.

How does it compare with a 70mm starter scope?

The 80mm lens gathers about 30% more light, so clusters and nebulae are brighter. The trade-off is a shorter focal length, which makes high-power planetary viewing harder.