Al,
I have them and they are great. My advice, I would get them, well worth it. Much quieter and better insulating than my last SOB that did not have them.
This subject has come up several times in the last few months.
Here is a link to a previous thread with a lot of info about them.Hope this helps.
//heartlandowners.org/showthread.ph...e-windows-R-factor-and-added-weight?highlight=