I have a slightly jaundiced view of these scaffold tube "edge protection" arrangements. Rarely is there any "toe board" or other provision to stop falling materials, as you say mid-rails are conspicuous by their absence and the process of erecting and striking these tubes at the roof apex is rarely carried out in compliance with WAH Regs.

Far better to return the working paltform around the gable with platforms at appropriate height to mitigate the effect of any fall - just as is done at front and rear elevations.