If I ever make it as a Warfare Officer I hope to specialise as a HM too. I think it sounds like a fab job! Interacting with nature at its finest, surveying the oceans and coasts of the world, getting the chance (although a very slim one) to serve on HMS Endurance- what could be better?
I have heard it described as the fluffy side of the Navy but you will leave with qualifications recognised as a civilian. People such as the BAS actively seek out people who trained in the RN.
I think it sounds awesome, and if I get my commission I might be serving along side you one day in the not too distant future.