headers: flexible parts?
 

because the aftermarket collectors do not have the two flexible parts of the original?
It is not necessary? that function have?

1. cost
2. if it was necessary they would all have it.
3. nvh noise vibration harshness
4. eventually the part will fail, flex pipe will reduce vibration and make the part last longer. but braided flex pipes also fail when they leak/rip etc.

to be calm without flexible areas?

I do not understand.

we can rest assured installing aftermarket headers without flexible areas?

Buy a good brand with good materials and fit and install correctly and you are ok.

ok, thanks ;)