Swinger has choice about complete uniform (8)
I believe the answer is:
pendulum
'swinger' is the definition.
(something which swings)
'choice about complete uniform' is the wordplay.
'choice' becomes 'plum' (both can mean excellent).
'about' is an insertion indicator.
'complete' becomes 'end' (I've seen this before).
'uniform' becomes 'U' (phonetic alphabet: alpha, bravo, charlie etc.).
'end'+'u'='endu'
'plum' placed around 'endu' is 'PENDULUM'.
'has' acts as a link.
(Other definitions for pendulum that I've seen before include "Old time swinger?" , "Lead swinging" , "Swinging part of clock" , "Swinging weight that regulates clock" , "Oscillating part of clock" .)