Is the Galaxy S21+ still worth buying?

Yes if you want a large 120Hz screen and solid battery life for less than a current flagship. It no longer gets Android version updates, so security and long-term support are the main limits.

How does the S21+ compare with the S21 Ultra?

The Ultra adds a 108MP main camera, a longer 10x zoom, a sharper 1440p display and S Pen support. The S21+ is lighter and simpler, with the same core chipset.

Does the S21+ have a microSD slot?

No. Storage is fixed at 128GB, so plan around cloud storage or a phone with more built-in space.

Does it work with US carriers?

The unlocked model works on AT&T, T-Mobile and Verizon, including 5G where the carrier supports it. Check that the unit is carrier-unlocked before buying.

What comes in the box?

Samsung ships the phone with a USB-C cable and a SIM tool. There is no charger or earphones.

Is a refurbished S21+ a good idea?

It can be, since the phone is older and refurbished units cost less than new ones. Check the battery health and return terms, because wear varies by unit.