don’t have all that much to tell you except I don’t like the effect.
You might want to get the classic macro book by John Shaw
“Close-ups in Nature” which covers flash very thoroughly and is
probably the classic book on macro photography. You should
have a copy at any rate.
Viewfinders Are About Light
A camera with a bright and clear viewfinder is important. Modern
DSLR cameras offer viewfinders that are larger and smaller,
meaning that some cameras show most (but not all) of the
subject frame while better ones do show all of it. If you can, get a
camera that will shows 100% of the frame. Prism-based
viewfinders are called OVF (original view finder), while the newer
electronic viewfinders are called EVF.
Electronic viewfinders are still just being perfected so it may be too
early to depend on them. The same goes for the LCD preview
screen on the back of the camera. These LCD panels when used
in LiveView can be helpful for certain kinds of focusing and for
enlarging areas of focus but for most work they are not a good
substitute for a large and clear viewfinder.
Full frame sensors (FX) tend to have larger viewfinders than the
smaller DX sensors, so you may what to keep that in mind.
Recently the Nikon D810 was released, with an updated LiveView
that is IMO better than any EVF I have yet seen. With the D810
LiveView I can finally see to focus and magnifying what I am seeing
as much as I wish.