Instant benefit, getting hold of singular hair styler (6)
I believe the answer is:
mousse
'hair styler' is the definition.
(product for styling hair)
'instant benefit getting hold of singular' is the wordplay.
'instant' becomes 'mo'.
'benefit' becomes 'use' (I've seen this before).
'getting hold of' indicates putting letters inside.
'singular' becomes 's' (abbreviation sometimes used in dictionaries).
'use' placed around 's' is 'usse'.
'mo'+'usse'='MOUSSE'
(Other definitions for mousse that I've seen before include "Frothy dish - hairdressing" , "cold dish" , "Frothy, creamy dessert" , "For us, some kind of dessert" , "Fluffy pudding" .)