Thats all I use in my street rods. I put it in the upper hose and lose very little fluid when I change it out for the winter restrictor. They work for me and also eliminates a problem of one sticking and burning up a motor.
Many people used them in the old days...Some still do. The problem is NOT too much water, it is getting enough that does not have air mixed with it.(aireated) Stock water pump impellers were not designed by people that really knew what was needed. They aireate the water especially at high rpm....Air is a very poor conductor of heat when introduced into a water cooling system. Several people have redesigned the impeller and convert flathead pumps. They really work. You can run thermostats and never boil even in the hottest weather as long as you have the rest of the system in good shape. Skip Haney's pump conversions are one of the best known.
The Jalopy Journal
