Cisdem PDF Converter OCR 6 is on sale for $19 via Mariner Deals, so I gave it a test vs. my current OCR tool, an old (v. 9) version of Adobe Acrobat Pro (included with my scanner when I bought it several years ago). The Cisdem demo will work on up to 3pp, so I processed the first 3 pages of a PDF from a 600 DPI scan of a book, including a title page with vertical and horizontal lines and text, the copyright page with some centered text and a paragraph of normal text, and a page from the TOC. I was converting the scanned PDF to a PDF with text. It was from a math textbook, so not the most common English. Some comparisons from this one text:
* Both apps deskew. I didn't see deskew mentioned anywhere on the Cisdem web site; it's important and they really should mention it (I almost didn't even try it because deskew wasn't mentioned). In deskewing, Acrobat appears to favor vertical alignment and Cidsdem horizontal alignment, e.g., on the title page, Acrobat accurately fixed a full-page vertical line, but was less accurate with a 3/4 page horizontal line. Cisdem did the opposite. Subjectively, Acrobat's deskew seemed slightly better on all the pages. Cisdem's deskew gave results that were more obviously inhomogeneous (e.g., aligning one side of the page nearly perfectly, but the other side less so).
* Both apps recognized letters with high accuracy, with Cisdem occasionally missing a space between words, but otherwise matching Acrobat in accuracy.
* Cisdem recognized the Roman numeral page numbers accurately. Acrobat failed here; it translated "vii" as "Vll" (those are "ells") and "ix" as "IX", for example. Both recognized Arabic page and section numbers with equal high accuracy.
* Acrobat optimizes as part of its OCR; the final file was 53% of the size of Cisdem's. The visual quality was very similar between the two; if I had to choose, I'd say Acrobat looked slightly better, despite being half the size.
Of course, Acrobat does a ton more than PDF Converter OCR. But if you are only interested in OCR, at a fraction of the cost of Acrobat, Cisdem's app is very competitive (with what you save vs. Acrobat, you could also get PDF Expert, ending up with most of Acrobat's capability yet saving $40, or more if you catch sales). The factor of two in file size is the main weakness of Cisdem.