Some years ago, I used it for quite a while in an Mitsubishi engine in a Caravan. I feel it worked well. But, don't try it unless you are something like a perfectionist and do it right. Also, if a hose ruptures when you are on the road, you will have to start over again. The advantage is not that the overall head temperatures will fall, but that it handles temperature spikes in isolated spots, which can be up to 1700 degrees in a racing engine, much better than the water mixture. I also feel that its degree of success will be different for different engine types.
I currently use either Sierra or Prestone's version of a PG product in 2 old vehicles. These products are mixed with water and offer no cooling advantage (actually a slight disadvantage). The only reason I use them is that the vehicles have been burning a little bit of coolant in the engine for years (I would guess due to a head gasket pin hole leak), and the PG will not damage the engine like EG will.