Comments on Rigid-Flex vs Flex with stiffeners - What is the practical difference?

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Rigid-Flex vs Flex with stiffeners - What is the practical difference?

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Looking at Flex-Rigid PCB technology vs Flex PCB with added stiffeners under sections with components I struggle to see the advantage of Flex-Rigid for low layer counts, as it seems more complex to manufacture and is more expensive as a result.

There is a lot of information online explaining what Flex and Flex-Rigid is, but I could not find many discussions about the advantages for one over the other, just some claims like 'Flex-Rigid is more reliable' without explaining how or why.

The only thought I had was that rigid allows for high layer count. Is there more to it, could someone please explain with some real world examples when one is more appropriate than other and why?

Edit: Let me expand on the definitions of Flex-Rigid and just Flex with stiffener.

Flex-Rigid:

diagram cross-section of a flex-rigid PCB photo of a flex-rigid PCB

Flex with stiffener: diagram cross-section of a flex PCB with a stiffener photo of a flex PCB with a stiffener

So in the Flex-Rigid case flex part is integrated in rigid part, whereas Flex with stiffener is just a polyimide with FR4 or similar material to reinforce certain sections, but the stiffener itself does not provide electrical connections.