“Composite sheva” is a term used by KHW to refer to the vowels given here:
It seems that every grammar invents their own name for these. Some call these vowels “half” or “reduced” vowels; others “very short vowels” or “compound shewas”. Then, some use the terms given above with the hataf-. These are all different names for the same reality.
Gutturals prefer these kind of vowels to a simple sheva. more