Ours has them. Make a diff for sound-proofing from noise outside and also do some good with heating or air-conditioning but just how much I don't know. I would not have single pane windows, being used to the double pane. Been in trailers with single pane--you can tell.
Two of the windows did lose their seals right away but the trailer was still under warranty, so that got fixed. (whole windows were replaced) No trouble with any more in the eight years since.
Our first trailer had those black sort of windows but this one has clear. Much prefer the clear glass too.