Good question mate, and you may know more about the answer than I in your Ambo line of work, but once the core of your body is warm, the extremities sort themselves out. With nice warm blood leaving the core, you stay surprisingly warm for a long period of time. I have experienced both this situation (leaving Silverton NSW -1*C) and the opposite (leaving Griffith NSW 0*C). Silverton I had the vest and barely noticed to cold (except nose/face etc - jacket ON) Griffith - NO jacket. Was warm for around 40 mins until the "cold to the bones" feeling won over and didn't really enjoy the ride for the next 3 hours until temp got over 6*C and sun was up.
A huge difference in riding comfort and therefore less distraction etc.
Can you tell I'm a fan? lol
For $149 and living in Tassie - it's probably worth it for the Aussie made wonder - you can even wear it to the footy, or around the yard etc.
Hope this helps.
Cheers, Diesel