I've never used 40 Below---I have used Water Wetter in my cars for years (it's in the Vette)--the idea is these products improve heat transfer. I guess the question is are they "snake oil" ?? hmmmm... in my case many years ago i added water wetter to a '62 Plymouth we owned, the operating temp dropped 3-4 degrees as i remember in the summer heat. That's what made a believer out of me.
Now it's a part of what i add when i do a flush or drain and refill just as a part of maintenance.
A few things to keep in mind ,these cars run hotter by design then most people are used to seeing. If you're not sure of the service history on your car---then a flush or drain and fill is always a good idea. Also be sure the the ac condenser and radiator fins are clean--these cars do collect debri from the road such as grass,leaves, plastic bags etc. Look close at the area between the condenser and radiator. Here's a interesting link about water-antifreeze and the above products
Vaughn