Yea.. it'* a hidden Gem..
the 0 is cold start vs. 10W.. which means it'* thinner when cold.. so it helps in winter as the oil gets to all the moving parts quicker.. next time you have 10w-30.. leave it out in the cold over night and pour it.. you will see it'* slower to pour and thicker due to the cold. Cold start is the worse for the engine as the oil hasn't circulated and lubed all the moving parts.. so to me.. I want something that will get flowing quicker. Now it may consume a lil more oil cause due to the thin nature during cold so you may get some pass the piston rings and burnt off during start.
30.. well thats the up to tempreture.. and our cars run on that.. so thats the only difference is the cold start. Walmart sometimes carries Esso XD-3 0w-40 but its a lil too thick @ operating tempreture for my liking and it will affect your MPG.
I always run between half to a quart lower then full top up 4L vs. 4.5L cause IMO less of the rotating crank is slushin thru the oil pan, so creatin less resistance.. but thats just my thing