As Aneesh said, Ace should delete the temp files automatically. So if you had to delete them manually, it means AU crashed.
The temp files in the free space of the disk do not take any space. It is just random data. A newly formatted drive also has meaningless data (random or zeroes).because if some amount of temp files can be restored, that means that those temp files are still on the hard drive somewhere and they are taking free space
After the free space wipe, there will be an entry (a random file name) in the file table pointing to that location, that's all. That's why some recovery tools list that file. But no one will be able to recover ANY data.
We won't be able to update free space wipe in this version to not show even those temp file names.
We will implement that in the next update. Only problem is this method will not be able to wipe the system drive (C: normally) like the program you've mentioned . To do that, we will have to create another exe that wipes it from a boot floppy/USB/CD. Won't that make AU complex?