No interference with cardio belt also Bluetooth 4.0.
Call quality is good even on FaceTime.
I had to install the biggest tips to avoid losing them and comfort is total, what freedom !! Uses almost no battery such.
Minor drawbacks, the position of buttons on the left atrium is therefore as right handed, it will take a little time to adapt.
Second downside, I can not use Siri because the microphone used remains that the phone apparently :(