I've worked with both ... as I said in your other thread I just don't care for the C79, it just doesn't have any balls. It's a critical listening midrange for people who are primarily concerned with fleshing out detail at low to mid volumes. Me, I like to blast music sometimes ... if it can't also get obnoxiously loud while still staying clear and composed, it's not for me.
The C79 is like the hubble telescope watching a concert, sure you see all the fine details but you're still stuck in a lab with no emotional connection. The 12m puts you in the front row of the mosh pit, sure some detail might get lost but you remember the experience a lot more.
The C79 is also a lot more difficult to implement properly, and it's a pain to router a cutout for

If you want more detail than the 12m but still keep the balls and that emotional connection, checkout the Seas W15CH or CY. If you want to try Accuton, maybe one of the larger cone drivers would be a more emotional midrange thanks to moving more air, but I haven't worked with any others than the C79.