How long does the battery really last?

Kenro claims 68 hours of use, which almost certainly counts recharges from the case. Expect the buds themselves to run for several hours per charge and the case to add many more.

Is the noise cancelling good enough for flights?

Active noise cancelling helps with engine and fan drone, but budget ANC usually lets voices and sudden sounds through. It is better for offices and buses than for loud cabins.

Can I use one earbud at a time?

Most earbuds in this class allow single-bud use for calls, but check the manual. Mono mode is common and useful for staying aware of traffic.

Do they work with iPhone and Android?

Yes. They pair over standard Bluetooth, so they work with iOS, Android, Windows and Mac. Some features may need the vendor app, if one exists.

Are they good for running and the gym?

There is no published water-resistance rating, so treat them as everyday earbuds. Sweat and rain are a risk; use them for commuting and desk work rather than hard workouts.