Decided to take the tubes for a spin. I think I'm quite happy, now. Much less frustration than with a reversed lens, plus, provided nothing is obstructing the flash, the flash works well.
Working distance is still a bit short, so a very nervous insect may not be an easy shot.
1) Fire Ant.
2) Another view of a fire ant
3) Unidentified Insect. About the size of the ants. Looked right at me as I took his picture, then quickly ran off when the flash fired.





