Don't expect WW to make any temp difference on a system that is working properly. If the thermostat is not all they way open, then the increased heat transfer will only cause the thermostat to vary its opening slightly to adjust. You would not notice that temp difference, or at least I doubt it.
However, if you max out the cooling system and the thermostat is all they way open, then it can make an actual difference in the temps.
As to how much difference it makes in a normal street 50/50 application, I'm curious as well. I use it from time to time when I perceive a cooling system to be less than overkill for my application.
I have never had problems with it FWIW.