Restriction heading off or that's the impression (9)
I believe the answer is:
imitation
'that's the impression' is the definition.
(thesaurus)
'restriction heading off' is the wordplay.
'restriction' becomes 'limitation' ('limitation' can be a synonym of 'restriction').
'heading off' means to remove the first letter.
'limitation' with its first letter taken off is 'IMITATION'.
'or' acts as a link.
(Other definitions for imitation that I've seen before include "False" , "Mock -- ersatz" , "A copy of an authentic item" , "Sham - mimicry" , "take-off's called for!" .)