In a review of my own experience with the Smart Data Recovery product I expressed surprise that of the many listed files apparently recoverable the vast majority were not.
Alexander Rodichev, CEO of Smart PC Solutions, which produced the product, sent me this information about his company's product's behaviour:-
"The reason you see 30,000 deleted files is because when you run Windows on the PC, especially if you have had the PC for a long time, it creates a lot of files as you are working. Lots of temporary files will also result in you finding lots of deleted files when you run the search.
"When you de-fragmented your PC the files would have been overwritten, but information about their names would still remain – and therefore show up in the search.
"The fact that only .txt files were readable may well be because many of the other documents would be much bigger, in which case some parts of the file may have been overwritten at some point, meaning that they couldn’t be opened. This would also be the case with the USB stick – if any part of a file has been overwritten then, unfortunately, it can’t be restored.
"Regarding your other point that people could restore other users’ personal information from a USB stick that had been found or stolen for example, the company also has a free product called Smart Data Scrubber http://www.smartpctools.com/data_scrubber/index1.html that enables users to completely remove details of any files they have deleted so that they can’t be restored, even with a data recovery product."
I'm happy to pass this information on. It confirms my view that the product is best used for the attempted recovery of newly deleted files.