https://www.tindie.com/products/movsensllc/trackimu-camera-free-head-motion-tracker/

https://www.kickstarter.com/projects/625849435/trackimu-camera-free-wearable-head-motion-tracker

Features:

3 Axis Rotation Tracking (Yaw/Pitch/Roll);
Compass sensor integrated, zero-drift in Yaw;
9DOF IMU (MPU9250) + Barometric pressure sensor (BMP280);
Arduino processor integrated for on-board signal fusion, and customized application development;
Direct talk to games - USB Joystick Emulation.

And available at 65$. Not bad looking at all.

Engadin.

Seems similar to EDTracker .... don't see "6DOF" movements - lean and zoom.