gary im a big guy.6ft 2 in and 17 stone(not fat though anymore!)work out at the gym a few times a week(bike,free weights etc) but even i know its common sense to use the best lightest equipment you can afford when your poling all day on various different properties.
no point making your working day harder is it?
i dont believe in being a cheapskate when it comes to tools for my business as it makes me far more productive and its reflected in much higher earnings over the last few years.best thing ive done for my business! 
My days are very easy generally

Lighter gear makes sense especially to what we were forced to use
less than a decade ago but some of the difference in weight of these
brushes are now changing at tens of grams not hundreds and there
is only so far you can go before you lose cleaning power and you have
to increase the movement yo to make up the difference and
so increase chance of RSI injury.
Seems to counter what you are trying to achieve far as im concerned
gardiners sill brush is light enough far as im concerned and not far
off the cleaning power of the vikan sill