The File Manager feature is a very handy design at Site5. I used that to create new folder, nevigate and even move files around. That could almost replace your ftp client except for file uploading. The only downside would be the response could be sluggish and you may only see a portion of the file path display on the right hand pane if you go really deep into your directories.
The file uploading doesn't appear to work. I saw no error message but after refreshing I still don't see the file uploaded.
For testing of file download I have created a directory "\downloadable" under \public_ftp. That could be accessed via ftp://ftp.mydomain.net/downloadable/.