Machine used in too many designs, on reflection (6)
I believe the answer is:
dynamo
'machine' is the definition.
(dynamo is a kind of machine)
'in too many designs on reflection' is the wordplay.
'in' indicates the answer is hidden within the clue.
'on reflection' is a reversal indicator.
'omanyd' is hidden within 'too many designs'.
'omanyd' backwards is 'DYNAMO'.
'used' is the link.
(Other definitions for dynamo that I've seen before include "Electric current producer" , "Type of electrical generator" , "Energetic person (colloq.)" , "It generates electricity" , "activist?" .)