Here is a demonstration of Jazz splitting in half. It looks like there is a latch on the lower half of the torso that has to be released to allow the split.
Definitely getting Jazz. Megatron looks good, but I'm cagey about it because I'm wondering if I should hold out for a different iteration of Megatron, even though it may take a while to show up because Hasbro/TakaraTOMY seem to be going through characters one movie at a time.
It looks like the split occurs where his waist rotator would be, so I doubt the figure was compromised to allow this gimmick.
As for details, my guess is that the Human Alliance figure was compromised due to its need to have a working cabin that a figure could fit in. The Masterpieces have no such requirements.
Still, the HA Jazz is in my opinion the best currently available movieverse Jazz.
Every figure in the restarted Movie Masterpiece line has diecast in it. It looks like Megatron has it in the fuselage - notice how the section of the fuselage between the wings in fighter mode is a different colour to the surrounding plastic.