As far as I know - nobody does this is any more. Manufacturing techniques and better quality control make adding certain additives unnecessary or harmful.
Usually you should not need to add this stuff - if you need stop leak, you should fix the problem right the first time and repair the damaged component. These types are products are more of gimmick than anything else. Sure they might plug up that small hole in the radiator - but what of the cooling passages in your block? cylinder head?
Water coolers works best will de-ionized water. They are ideal for race engines which need the ability to shed extra heat. They can work with a mixed solution of antifreeze and water - and some have seen big decreases in temperatures (as much as 30 degrees F with pure water).
Unless you have overheating issues while driving through hot climates - I wouldn't bother at all with adding anything to your cooling system.
The main reasons for mixing water and coolant together is for increased thermal conduction, corrosion resistance, increased boilover protection, and lower the freezing point. Run just plain water and a water wetter may be good for a race track - but less than ideal for around the town driving and highway use. The thermal flexibility and range of a good water and coolant solution is why most cars on the road use that.
Plus most modern cars are tested in very adverse temperature ranges as they are being designed - if they really needed a water wetter or temperature modifier - then they didn't do their job right.