Conclusion: Good headphones but the low whistle is annoying although I think getting used to over time.
To make it work under Linux (Debian gnome Jessie & 3) I had to install "apt-get install pulseaudio pulseaudio-module-bluetooth pavucontrol". Then reboot and the helmet was well recognized in time as audio device. Of course, I had the equipment before. Remember to choose the profile for the HD audio (A2DP)!