I'm using what I think is the latest GPO Studio "beta" (GarritanStudio0003.zip) which I saw around here on the forum, if I recall.
It seems to be more stable than the previous or 1.2.
However, I have some usability suggestions. When you "open" a file, it loads. There is no way to tell what file you have opened. There should be something in the display or title bar that tells you the file name you last loaded.
When you want to save changes with the "Save" button, it pops up a panel that says generically "File exists. Overwrite?" But that doesn't tell you the file name! Egads, you have to remember what you last opened, and whether you really want to overwrite something. Furthermore, when you hit "save" the panel's title is "Save as..." I think that's also a bug.
If you try to quit, the program asks, "Save changes to Foo?" (assuming you opened "Foo.studio"). So, the application does remember the filename. Presumably, it could display the name in the UI and/or ask you "File Foo.studio exists. Overwrite?" when you save or quit.