Tom Brinkmann, the creator of Bad Mags, explains what the site is about in his intro on the site:
The main reason I wrote Bad Mags was because I wished I had had something comparable when I started looking for and collecting these magazines--a guide if you will. Because Bad Mags attempts to cover such a large selection of subject matter any chapter included in it could have been its own book. Bad Mags is not a complete listing of the magazines and tabloids covering these particular subjects (if such a thing were possible), but is an attempt to give a more complete picture of what was published concerning them at the time.
Beyond that Bad Mags is a book devoted to strange, bizarre and peripheral magazines because the back alleys of the publishing industry have been little explored in print. In most cases there isn't any information readily available, limited only to the information given in the periodical itself.
There's more, visit the site for the rest. As Brinkmann says, the site is "a carnival of covers." Not only covers, but Brinkmann gives a lot of good background on each category. You'll spend a lot of time over there; a lot to look at!