I have the Unterwassertasche been used once in the Baltic Sea while sailing. There was not to think of underwater photos because it was too fast dark. The water was probably not clear enough and the cloudy sky. But floating out of the water, you can still make great photos !!
The bag is quite easy to use and really tight. It becomes difficult, if one wants to make adjustments to the camera - so it's better to operate the camera in automatic mode. Then you have to sensing only the shutter :)