The best in ear wireless headphones deliver excellent sound. The bass, treble, and mid frequencies should maintain their clarity even at high volumes. The listener should be able to hear every instrument and every voice without difficulties.
They are also quick to connect via Bluetooth. The signal is stable within the prescribed range as long as no obstacles get in the way. The left and right side should be able to pair every time for stereo output.
The ears must remain comfortable even after wearing the headphones for a long time. Indeed, the unit should have a battery that will allow it to stay charged for several hours before needing a boost. Three hours is common in low-cost options. Advanced models can manage more than 10 hours.
It should also be stable enough for running and other sports. Some people might even demand waterproofing such that sweat will not be a problem.