Quexos, my theory is that they're free so if after you've read the blurb on the book - and you like the sound of it - then download it.
If after reading some of it you don't like it - then ditch it.
Having said that the free books I've downloaded the most of are The Classics and Free Mysteries.
Some of the free mysteries are authored by the initiators of the Genre eg. Mystery of the Yellow Room, Leroux; and The Moonstone, Wilkie Collins.
However - you're also bound to be able to find a lot of these books on other sites that have free books, like Gutenberg et al.
Enjoy
