They are right in regards to gaining more diving experience before diving with a camera.
That being said, I suggest using the camera in a pool or water environment so the magnification and color loss can be better understood with your camera and strobe. The biggest problem I see is the diver being too far from the subject due to water magnification. As an example, your arm is maybe 2 feet long and can be used for reference when measuring, but even then, the light has to go from the camera to the subject and back to the camera again, so you have over 4 feet of water and are already loosing color. A camera strobe is only effective for a few feet in water.
I cant count the number of times I have handed my camera to a divemaster for a photo of my wife and I, and he moves back so far the photo has no color. I motion for them to get closer but without camera experience or training they dont want to get close enough.