The magnet can be used in any metal pan. My 92 Chevy Astro has a magnet in the trans pan from the factory. When I do a trans fluid change, I clean the magnet and trans pan. The magnet does a great job of collecting metallic debris. The rear differential on my Chevy Astro also has a magnet from the factory that works very well on collecting metallic debris.
I changed the trans fluid and added the magetic on my 98 E320 at 80K miles. The fluid was filthy and the bottom of the trans pan had about 1mm of sludge - I also recommend the 60K trans fluid intervals.
1998 Mercedes E320, 200K Miles
2001 Acura 3.2TL, 178K Miles
1992 Chevy Astro, 205K Miles