"Do flash cable adapters make sense?"
In actual fact every underwater photographer should be ready for emergency cases. It is better to carry something with you and not need it than vice versa. With the appropriate cable adapter you always have the option of borrowing a flash from a colleague or the dive base. This however is only possible if the connections are adaptable. A SEACAM S6/N5 adapter can save your trip and you can continue using manual flash.