As a novice window cleaner I am always practising and hopefully learning.
Cleaned the bathroom mirrors using gg4 some time ago, they came up great but within 2 weeks of kids long steamy showers the mirrors were oozing the solution and filthy with runs all over. Did them again using gg4 and the same happened.
Did them again with a mix of Mr Muscle and water, squeegeed off, came up perfect and have stayed that way a month later.
LESSON LEARNED: Beware of gg4 in steamy/damp areas.