Does the Shein Smart Ring track heart rate or sleep?

No. It is an activity counter with a color screen, not a health tracker. There is no heart-rate sensor and no sleep tracking.

Does it need an app or subscription?

No app or subscription is required. Stats appear on the ring's own color screen, so there is no synced history to review later.

How does it compare with an Oura Ring?

They are not in the same class. Oura tracks heart rate, sleep, temperature and readiness with an app and subscription; this ring only counts basic activity.

Shein does not state a water-resistance rating. Treat it as splash-resistant at most and take it off for swimming or showers.

What sizes does it come in?

Sizing is limited and the ring is not adjustable. Check the listed size guide before ordering, since a plastic ring cannot be resized.

It can work as a first step counter for a child, since it is simple and has no app or account. The plastic build and lack of health sensors suit casual use.