Used it the other week but from a different supplier. Slightly different U Values but more or less the same thing. I had it with Krypton gas and fitted them to existing sash windows. Had to rout out rebates deeper and exchange cast iron weights for lead. It wasn't a bad job in the end but there is better ways to skin this cat. New sashes, smaller moulding and deeper rebate for more standard units (12mm spacer)