No software will ever give you 100% guarantee
. But, if you delete a file, Recuva will find it and recover it. If you delete a file, then erase the free space on the drive, Recuva will not be able to recover that file; I have done this dozens of times, and the results are consistent.
That said, the NTFS file system is a very complex beast, and my experience is that, certainly the first time you wipe free space, there will be odd files residing in space which Eraser does not necessarily treat as free, and therefore which Recuva can find; sometimes these files are recoverable, sometimes not. So, after your first free space wipe at least, it makes sense to run Recuva, and use the facility in it to overwrite any files it identifies. With that technique, I find that drives (particularly non-system drives) become progressively cleaner, to a point where they contain at most a couple of recoverable files.
In all of this, the real risk is not that Eraser will fail to erase what you tell it to erase. The real risk is that you do not (or, in some cases, cannot) recognise all the locations in which the file system, the OS and individual applications have squirrelled away data that you might regard as sensitive. To guard against this
- do not delete sensitive files, erase them;
- run a free space erase once in a while to clean up after deletions you may not be aware of;
- if you defrag your hard drive, wipe the free space afterwards; defrag leaves behind the original data of any file it moves;
- completely erase all drives before you let them out of your ownership or control.
I hope this helps.