The status of this record is a bit unclear to me. It is based on the demo tape that the Metallica made before their first album, back in 1982. The first seven songs were coming from this famous No life ’till leather demo tape. Conveniently, they made another demo tape in the same year, and that was called Metal up your ass, but it contained different songs. All of these have never been officially released.
And it is not for lack of trying. However, the second song on this album, The Mechanix, has writing credits by Dave Mustaine, who was lead guitarist in those early months. Mustaine turned out to be totally misbehaving and under constant influence of either drugs or alcohol. He got into multiple conflict with everyone in the band, until it was decided to fire him. Mustaine moped around for years about that, and started Megadeth as a pissing contest to see who could play the fastest.
In those years the relationship between the two thrash bands was challenging at best. To share writing credits for this song was too much to ask, and it never happened. Megadeth has the same song on their debut album. And of course it was played faster.