"Note: CCleaner can only securely delete files which have not yet been deleted from the Recycle Bin"
That makes the "Wipe Free Space" option in Cleaner and the "Wipe Drive" option in Tools very misleading. Disk "free space" is commonly understood to be those blocks which have no entries in the File Allocation Table (FAT). In fact strictly speaking "free space" does not include the space taken by files in the Recycle bin as they do have blocks allocated to them albeit not in the usual way.
Most users who want to wipe free space are not concerned about the files in the Recycle Bin which they know can easily be recovered - they are concerned about files and file fragments that are still on the disk but which the system considers deleted. There are plenty of tools available to recover (in some cases partially) these files. So there is little point in "wiping free space" using the Guzman method (35 passes) if these files are still recoverable.
I strongly recommend one of the following options in order of preference:
1. Implement full wipe free space functionality
2. Rename these options e.g. "Wipe Free Space" --> "Wipe Recycle Bin"
3. Ensure that users are warned of the limitation of these options via a pop notice at the time of execution which clearly and explicity states that only files in the Recycle Bin will be securely deleted.
I am also quite surprised by how long it takes to "wipe" the Recycle Bin even when it is almost empty - it took over 20 mins to wipe a 1 kB file !!!
If I have misunderstood the funcitonality of the "Wipe Free Space" and "Wipe Drive" options please correct me.