Ours has dual pane frameless windows. The dual pane were optional and they work great.
Kinro.
All of our frameless windows open from the bottom, have screens, and while they let airflow through they don't let rain in, so I'm not understanding why some folks would feel like they don't let air in. The larger windows have a top fixed pane and bottom tilt out pane. You don't get the "rotting" and "splitting" gasket that you get with the standard windows after a few years in the sun.
Not for everybody I guess, but I sure like the looks of them and would hesitate to get one without them now as it would look dated. Some even have matching see through graphics over the windows that make them invisible from the outside - kind of cool.
Just a note: I have not seen them in the side of the slides. I suspect they don't slide well through the slide seal. Ours has dual pane standard sliding windows in the sides of the slides.