Krypton gas windows are being sold under the claim that they help insulation far better than plain air-filled windows. This is true of both Krypton and argon-filled windows. The gases are pumped into the crevice between double and triple glazed windows and can also prevent condensation build-up.
Pros of Krypton
Compared with argon gas, krypton is far denser. It offers excellent thermal efficiency and should not leak out of the windows if they're constructed properly. It does not pose a threat or danger if it does leak out. Krypton reacts well as an insulator in both winter and summer conditions. Krypton gas has properties that make it far denser than our own atmosphere, which helps with thermal protection.
Cons of Krypton
As Krypton is one of the least accessible and most expensive gases in the universe it is not the most economical choice. As it only consists of 1 part per million in the atmosphere, it is extremely rare compared to other gases like xenon and argon. This makes it a high-cost investment, so when considering the costs of gas-filled windows, think carefully about the overall protection and convenience of paying for Krypton when xenon or argon would suffice quite well.