This is a three cassette bootleg from 1997, back before CD recorders were common. In a post to alt.music.marilyn-manson, Gagfish described it as such:

Gagfish Records still has a few copies for it's infamous box set SOMEONE
SUNG THESE SONGS FOR SATAN.  The 3 tape compilation contains every Marilyn
Manson and the Spookykids demo song, including each version, in
chronological order.  The set also has 9 never released tracks including
"Insect Pins" and "Magic Eight Ball".  All songsare digitally remastered
and are the best quality available - even better than the import CDs!  The
covers contain original artwork by Manson himself drawn during this era.
The set comes with a 5 page booklet explaining the history of the band and
these recording.THESE ARE NOT COPIES.  They are professionally
manufactured cassettes from the master recordings.

For a limited time this set is only $25 and postage is FREE.  Samples are
available on our website as well as our whole catalog and ordering
instructions.  Please check it out at www.gagfish.com.

The tapes weren't actually from studio masters, but they were from original Spooky Kids demos that Gagfish had obtained, or at least very low generation copies. Gagfish had the tapes professionaly duplicated for the best quality possible, and this set remains one of the best sources for Spooky Kids material. Unfortunately for Gagfish, his bootlegging operation got a little too professional and attracted the attention of the RIAA and he got shut down as detailed in this post. I was one of the people who had ordered a copy of this tape shortly before he made the announcement, but a few weeks later my copy arrived in the mail, and I was not disappointed.

The tape set also included an 8 1/2 x 11" booklet with a history of the band and a discography that was as accurate as anyone knew at the time, but now is know to have a few errors about the early material.