Retrofitting double hung sashes

I'm looking at re-glazing my Victorian double hung sash windows with double glazing and I'm looking for a better system to hang them due to the added weight of the glass. I've also been looking at the way modern windows are made. Some use FSA "Mega Jambliners" which have internal springs which allows independent opening of each sash and others use the counterbalance method where they both open at the same time. I'd be interested to hear from anyone who has used either.
Attached Files

• http://www.renovateforum.com/images/attach/pdf.gif build-in-details-jambliner-dh.pdf (797.0 KB)
• http://www.renovateforum.com/images/attach/pdf.gif build in details counterbalance dh.pdf (735.5 KB)

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