Wow, that has some really bad user reviews.
By the by, Calibre is an eBook manager - it allows you to put things on your devices, keep a centralized catalog of eBooks on a computer hard drive, edit existing eBook files, and convert from one format to another (unless there is DRM in place, in which case you're scuttled unless you do something that is not entirely legal). This software appears to perform scans of a physical book into PDFs (essentially it takes pictures of the pages) and turns them into a eBook of sorts (one file with all those scans.) The results will depend greatly on how good that scan is (lighting, contrast, angle of view, etc.) so if you really work at it you might be able to get something decent, but it's going to take some work.
Now, if it could do very solid OCR (scanning the image capture and converting the picture of the words into text format words) it might be something, but there are comments on that specifically being poor. For $20 I'll pass, but thanks for pointing it out - I had not seen it before I read this thread.
- R