Insulated backerboards directly over studs?

[jacoscar]

I’m renovating my bathroom and I’m building a studwall behind the bath to accomodate some pipes and a concealed shower valve.
Do I need to have plasterboard beneath the boards?

Or can I screw the insulated boards directly onto studs?

https://www.diy.com/departments/qboard-basiq-square-edge-6mm-backerboard-h-1200mm-w-600mm/4025345158021_BQ.prd

If so, I guess I need to have studs at 300mm centres rather than 400mm