Spcifically duuble-hung, sliding ones. What people call "old fashioned
sash windows".

I've been looking on Mighton's site. I quite like the look of the
plastic parting bead, and the standard weatherstripping, to be installed
in 2mm grooves in the staff bead, the stiles of the sashes, or the front
facing of the boxes themselves. Not at all sure about brush seals
various, I think they will attract dirt and become unsightly very fast.

Any relevant experience?