Besides using step counter, could we know which function will you use in your application?
If you use G-Sensor on the head device, you could choose BMA456. If you use IMU on the head device, you could choose BMI270.
I think it is okay with any parts, but you need to test of course with our two algorithms.
Currently, we offer two algorithms for BMA400 which are for wrist and non-wrist.
In my opinion, non-wrist algorithm is more appropriate for head because it is more sensitive.
Page 43 in datasheet, you can check our algorithms and also you can test it 🙂
Hopefully, it helps you.