If the manual says use it then use it. Dual engine flame out is more harmful than the potential danger of pouring prist in the fuel.
And as stated, it is not about lowering the freezing point of the fuel but rather to make sure that the water in the fuel doesn't cause problems. Some engines have good fuel heaters, some have fuel filter de-icing capabilities (like the RR Viper) and some need additives.
If you are uncomfortable about using these additives you can sometimes get fuel with the stuff already in it (like Shell Aerojet). You can't get it everywhere but it is a way of lessen the exposure.