This is a potentially powerful tool, but it needs some basic upgrades to make it easier to use. The first is auto-range detection. VW should be able to auto-detect the range from lowest to highest - then let me decide 1 of 2 options - Stepped or Gradient. (User Defined Range option should remain.)
For Stepped - I would then select the number of steps - say 5 - and VW would auto divide the objects based on the auto-detected range. I then could assign the graphic attributes of each