gg3 is for soft water areas and gg4 for hard water.i use both squeegee off and gg3.i like both but i think the gg3 is a bit pricey compared to squeegee off.
the gg3 as less sud and not as much slip but the windows really SHINE!!S/O is more like fairy but not as sticky and is very good value.
i dont do much trad anymore so i think ill stick to s/o in future.
regards
dazmond