is the more flex the better? i was at an exhaust shop today and they had a used one, i could move around with my hand. is that supposed to happen? i think it was like about 6" give or take...

 

ttt..also interested

 

There are a couple kinds of flex pipes.
One with a braided steel wire cover and welded on ends (easy to weld to other pipes), and non covered ones that are a pain in the *** to weld to pipes.
Obviously, the flex pipe is intended to allow movement, so you don't crack welds or the pipes. So, movement is good. But you don't want a 3' chunk that is going to sag.
You also have to remember that the non covered stuff will rust like hell. So, less is more in that instance.