The 6am-9am arrival window into SYD is an EXTREMELY busy one. IME QF/VA/UA/DL arrivals with passports from either AUS, NZ, US, CAN or UK would be quite unlikely to even see a luggage xray let alone an actual bag search. You could get unlucky, yet the above is not the profile customs is looking for.

Go for regular TSA locks and you should be fine.