Mach Crit, Mach Number Buffet, Mach Tuck, and Mach Trimmers

[Panama Jack]

I think I understand the concepts individually.

However, I am having a bit of trouble trying to visualize them in interelationship to each other.

I understand that Mach Crit is where the relative flow initially reaches the speed of sound. However, if I understand it correctly, this does not necessarily result in a Mach Buffet (or does it). Instead, the aircraft becomes longitudinally unstable and tends to pitch nose down. For this we have Mach Trimmers, to allow for higher speed cruise by providing artificial inputs to compensate for the longitudinal instability. Am I right so far???

So then, where does Mach Buffet come into play?

Also, do modern jet transports regularly cruise at speeds above Mach Crit? Do all jet transports have Mach Trimmers or do some of them have good longitudinal stability above Mach Crit?

Thanks in advance for all helpful answers and discussion.