Testing using the slider in the Qt Quick Controls Gallery Example:

1. Using either the Jaws screen reader or NVDA screen reader, the value of the slider is not read by the screen reader.
2. Using the Narrator screen reader, the value is read, although when changing the value of the slider Narrator reads, for example, "slider at 0.4", rather than simply "0.4" which would be expected.

Further testing:

Using the slider in the Widgets Gallery Example, all the above Windows screen readers read its value.

Using the inspect tool to check the properties of accessible objects: 

1. For the slider in the Widgets Gallery Example, both the Value pattern and the Range Value pattern are set as being supported. And both the Value and the Range value are set correctly.
2. For the slider in the Qt Quick Controls Gallery Example, again both the Value pattern and the Range Value pattern are set as being supported. However only the Range value is set correctly. The Value is always an empty string. I presume that this is the problem.