I don’t ever judge a brush until I’ve been inside and looked at the windows “Upstairs” not down,on ground floor windows you can apply more pressure to the glass and it’s easier to scrub harder and convince yourself it’s a great brush.
The stiff brushes are a good example of this they look great from the ground but hit and miss and patchy on the upper floors,you want a brush that has a very slight flop on the glass to some extent imo the DuPont bristles give you this they will clean far better with cold water than any other material.