I've got to make a 45 degree elbow, is this stuff ok to use or is it pretty much junk?

 

I used it several years ago on an old Dodge and what I used was definately junk. It completely rusted within 6 months (the pipe, not the truck!).

 

Try not to cut corners when building an exhaust, because they are extremely susceptible to rust, and the flexy stuff will most likely rust pretty quick, just go down to your local exhaust shop and pick up a 45 degree elbow, they dont cost too much