On getting the Fotodiox extension tube set, I have tried using them on many subjects, with varying results.
Recently, I took pictures of a few bees as they entered and left their hive. As the tubes do not have any electronic control, the aperture is always set to the widest opening and that lets in a lot of light. This time, I was shooting in RAW + JPEG mode and having the RAW photos helped a lot.
The day was quite bright when I took the pictures. Hence man photos suffered from over exposure. But, RAW once again came to my rescue. Using the exposure control setting while editing the RAW file, I was able to retrieve decent images. These images were far better than the default saved by the camera.