I think about them quite sceptically, but what do you think, are they of any help to recover data from scratched CD-Rs or damaged HDs?

Yes, they are. Recently my first DVD->DivX rip died on a platinum CD-R. Windows didn't recognize the CD at all, so I tried several tools like BadCopy and the result was that the movie was sucessfully extracted to HDD. The last few seconds didn't work anymore (The CD-R was turned from silver to gold starting from outside, so the end of the file was more damaged and took most time to extract). If you store some error recovery information on the disk (like provided in RAR archive) I think these tools can help to get back the entire data that would have been lost otherwise.