I would agree to that when it comes to aluminium it can be better to have the flex joint that springs and rubber gasket creates, well they even use it for steel exhaust on full scale cars to avoid fatigue cracks.

The 2113 pipe should essentially be a 2069, I find them responsive at the bottom end with a good top end, that might be what they mean. It's always a problem when you try to describe something like this, so that all people no matter their knowledge will understand, from one sentence.