Going to put the cat amongst the pigeons here...
Remember that SH low fly in accordance with an AGL (above ground level) and MSC (seperation clearance), so an MSD is irrelevant.
Quite frankly, there is no tactical reason to transit low-fly at 50' as opposed to 100'. The small arms threat poses no greater threat at the higher height, and the DAS systems fitted to RAF and RN SH all need space below the aircraft to operate effectively. The tactical argument doesn't hold up.
Before you all launch at me, I do know what I am talking about because I am a QHI on an SH OCU.