Bristol use that. I've been led to believe that krypton and Argon do NOT mix, but stay seperated so that you get some area that are denser, where the krypton is and others that are not as dense, where the argon is.
Don't know for sure if that is truly the case or not.
Graef Windows also, or you can further upgrade to full krypton. There is a mega cost difference between the two and it is common to mix these to get a lower U value than argon.
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