No direct experience with Indows, but some related experience. We lived in Paris for a while, and were just amazed by the triple-pane, sound-insulated windows in many of the apartments there. You could be right on the street, close the windows and...silence!
Never found anything even close in the States. Other places in Europe, yes.
Now fast forward a number of years, we live in a late 1800's Victorian in San Francisco, on a lot that fronts AND backs on busy streets. After living in DC for many years, we were used to street noise. However, it became necessary to replace the (probably original) double-hung sashes in our front room. After pricing complete replacement windows, not to mention dealing with the City for permits...we decided instead to leave the original frames and just do the sashes. We went with double-pane construction, with inner one being laminated glass, so 3 total layers of glass. Supposed to do wonders for sound reduction, as well as thermal loss. Then we added plantation shutters on the inside.
Results re thermal gain are great -- on those rare hot days in San Francisco, front of the house is noticeably cooler. And drafts are pretty much gone on cold days. A win/win there.
Not so much on the sound-reduction front, though -- while it is readily apparent the sashes themselves allow less sound through, also helped by the shutters, a lot of street noise still penetrates through the windows and, more than we realized, through the walls themselves.
So now we think just replacing windows helps, but only some. If wall construction is such that it allows sound to penetrate (i.e. most stick-built houses) then just doing the windows is going to be of limited benefit.
In Europe, those buildings not only had super-insulated windows, but thick masonry walls, or timber construction with heavy plaster wall inside, etc., etc. The whole building was sound-reducing, not just the windows.
