Timestamp 35:18 "I copied this wholesale from Wikipedia, and I trust it because I wrote it." -Michael Shepard 

  

M-class means metal asteroids and there are very few of them. Seven or more depending on your source list. Many asteroids are ambiguous and hotly debated as to what should have it's own classification or go into one group or another.

I'm sure you know about Psyche. The $10 Quintilian floating iron-nickel ball. This video will touch on all there is to know about it and it's peers. Psyche, and also the second largest M-class asteroid by volume Kalliope, are as yet unexplored. All but Lutetia are un-imaged so far. Kleopatra appears to be one of the more relevant, and 758 Mancunia is most peculiar. 

• At 11:42 A slide for models.
• He goes into some stats at 15:30 You can skip to 52:00 to get the TLDR of this part but he's got some really cool slides that can be applied to many purposes. The slide at 17:30 really demonstrates the difference between having a probe or not. The slide at 18:50 implies that collisionally evolved M-class asteroids are likely debris off of the bigger planetesimal cores.
• The entree slide comes at 22:30. I want to let it speak for itself. But 758 Mancunia steals the show. Now that rock is an obsession generating mystery box to worry over. Also, let's take a moment and admit that both Anti-gone and Ant-tig-on-ee are both awesome sounding asteroid pronunciations.
• Much of the next few slides have a lot to do with radar physics. The key for those is that radar reflects best off smooth stuff, so smooth=white, rough=black. It's especially important with M-class asteroids because metals reflect radar particularly well. 
• Maybe the juiciest part is the stuff at 37:00 where he, like all others who make a good LPI video, suddenly realizes that even though he's delivering the good stuff, for some mysterious goddamned reason there's a time limit, and he starts skipping the the dessert of his lecture. That being the close-ups of Psyche. Then Lutetia (The only M-class seen by a probe so far) at 43:50. Then Kleopatra who is the upstager of the show. 

I wanted some more Kaliope, and find it conspicuous that there was so little. Kaliope is less dense, though bigger by volume, than many of the others, and that's a big deal in planetary science. There's lots of things that can cause it, and it applies to a lot more worlds than only Kaliope. Think Mars, Charon, Miranda, and Callisto. So it would have been fun to see some insight from something with funky density but still expected to have metallic content. I wonder at times if Kaliope has Vestoids mixed up in it. Something that can relatively date the two, or provide a timeline of their dismantling.