Years ago I bought an Almax Immobiliser III (1.5m) with Squire SS65 padlock and two MC4 chains (with padlocks). Had it all delivered to work (oh the days of work accepting personal packages). I certainly felt the panniers on the cycle commute home that day.
OK I got the Almax Immobiliser III. Jesus fucking christ, its fucking heavy...
FWIW I'm using it to secure a scooter...