The TOZO NC9 uses Bluetooth 5.0 to stay connected. Pairing and re-pairing takes only a few seconds to 10 seconds to connect. After initial pairing, the connection is almost automatic. This is because we all know how annoying it can be to reconnect earphones. Given that the NC9 is a basic product, it can only connect in the most common SBC codec or AAC, which makes it suitable for iPhone, but incomplete for Android. on Android, this is sufficient, but not high quality sound. on iPhone, the delay is minimal. Streaming video syncing is not a problem. Results may vary depending on several variables, including device type and video quality. As with the A1 model, ear tips are available in three sizes: S, M, and L. By default, size M ear tips are installed on the earphones. Most users are satisfied with the M size. However, if the default ear tips are not comfortable or do not fit snugly, they are probably too loose or too tight. Try replacing them with the other ear tips included (smaller or larger). Tozo T9 wireless earphones are ergonomically designed. Choose the right fit and snugness for your ears, and when worn correctly, you will feel a sense of stability. Even when running, jumping, or moving at high speeds, the earphones will not come off your ears at all. This is one of the best things about the Tozo T9s, and I am very pleased with the way they are designed to fit the shape of my ears.