Flexy rear frame mounts are the worst for header breakage. The header cracks like I think this one will, or if you're lucky enough to have it stay solid, the studs/exh screws will break off from even slight flex at the frame mount.
Spring mounted headers are the safest, but can leak if not done really well.
I've just seen lots of MLM header cracks even when no heating had been done and a solid rear frame mount,
I feel like pipe makers should use thicker header steel, I add a welded or brazed steel strap to the outside of some of my headers due to repeated breakages. Worst sound ever to hear when you're out far from home and you hear that distinctive header opening up "croak" then its louder and louder then its fucking awful (edited)