Motorcycle half helmets do not cover the face of the rider and are more open. This makes it more difficult to have a Bluetooth device that is voice-controlled because there is no part of the helmet close to the mouth. Also, because the face is much more exposed, there is more likely to be a problem with wind noise interfering with sound quality.
It is generally agreed that full helmets are best for Bluetooth connectivity and they offer a greater degree of protection. Full face motorcycle helmets with Bluetooth are always the best option.