I used one of those last month on a hunting trip in Montana. It was single digits below zero in the morning and the truck started like it was summer. I did have both the factory block heater and the oil pan heater plugged in.
According the a gm service bulletin, these engines can produce oil pressure in excess of 100 lbs. on a cold start(below 0) with 15w-40 oil. I was running 15w-40 and the oil pressure built up to about 80lbs when I started the truck on those cold mornings.
Hoss