Ultra-modern headrests advantage convertibles (5-5)
I believe the answer is:
avant-garde
'ultra-modern headrests' is the definition.
I can't judge whether this defines the answer.
'advantage convertibles' is the wordplay.
I cannot quite understand how this works, but
'advantage' could be 'van' (I've seen this in other clues) and 'van' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for avant-garde that I've seen before include "In the arts, radically new and daring" , "Experimental (art)" , "Radical - daring" , "New and experimental" , "Daringly innovative or unconventional" .)