I'm currently using this system without external flash for snorkeling and free diving photography, and the D2X/D2H/D70 cameras for land photography as well as a Nikon 5400.
I'd be interested in others' experiences and /or comments re the 5600 system here or via e-mail. In the future, there may be a housing for one of my SLR's which suits my needs as well..... (esp the D70 w Aquatica)