I haven't had the need to use a file recovery type program for many years. However, being as this app is free, out of curiosity, I decided to download it and put it through its paces.
As other posters here have noted, the first thing you will notice upon launching this app is that it screams "Windows!". If you are a longtime, diehard Macintosh user, you may find the UI offensive to your taste. However, I was more interested in the functionality of this program, so I overlooked the obvious attempt of a Windows programmer to make his software work on a Macintosh running OS X.
BTW, once you choose to begin a scan, the app's window opens fullscreen; so if you have a 27" iMac, expect the entire screen to be taken up by the app. Of course, you do have the option to drag the bottom right corner of the window to your preferred size.
The second thing that makes this app scream "Windows!" can be found under the "File Type" tab on the left side of screen. Under that tab you will find jpg, zip, jar, jpeg, doc, xlsx and docx. I assume that these are the default file types that the program lists after a scan is complete. I am not certain, because there is no users manual or built-in help with the app, as far as I can tell.
Being as this developer is a Windows user, it would seem that he chose these file types with little regard or concern for what a real Macintosh user might look for.
Personally, I extensively use BBEdit .txt files, Adobe Photoshop .psd and .png files, .dmg files, .pdf files, as well as .mkv, .avi, .mp4 and .flv video files, and .html files.
Not one of these file types is listed under the "File Type" tab, which in my view makes this app very unMac-like. They should be added. Likewise, for the musically-inclined, a wide range of audio formats should be added to the file type list as well.
For my test subject, I chose my 1 TB external drive which uses USB 2.0.
After scanning the external drive for files for about an hour, the app had still only done 51%. Above the progress bar it stated that it had found 1,871,622 files.
At that point, I got busy in my web browser doing other stuff. When I went back to this app again, just as other posters below have stated, the scanner had started all over again and was back at 4% complete. I wasted over an hour and a half of my time.
This app may be free, and it may work for some people, but given what I personally observed with its performance, I cannot currently recommend it with confidence.