We had fiberglass french doors (single side opening) when we bought our 80-s built house, they were not all one piece but made up of four pieces glued together around the glass. One day about 15 years ago (so the doors were about 20 years old) the latch side piece came unglued on the moving door, so we pulled the whole thing and replaced it with a slider (made more sense to us since it didn't open into the room). We turned the "fixed" half into the top of a coldframe where it still serves.
We built a 3-season porch 2 years ago, and put in a 5' wide set of steel french doors. I like them, but I can completely see Eddie's comment about the loosening over time. Not a security issue for us since the porch lock, but there is a slight draft on windy winter days. At the same time we reconfigured where the old french doors were by pulling the slider (and using it on the porch) and replaced that with a single steel door with built in blind. So far that has also provided very good service. These steel doors were all custom built, ordered through a local "builders surplus" place. The construction is very similar to Stanley steel doors, including the molding profiles around the windows.
We built a 3-season porch 2 years ago, and put in a 5' wide set of steel french doors. I like them, but I can completely see Eddie's comment about the loosening over time. Not a security issue for us since the porch lock, but there is a slight draft on windy winter days. At the same time we reconfigured where the old french doors were by pulling the slider (and using it on the porch) and replaced that with a single steel door with built in blind. So far that has also provided very good service. These steel doors were all custom built, ordered through a local "builders surplus" place. The construction is very similar to Stanley steel doors, including the molding profiles around the windows.