The JJ and Meg cans are both anodized. They dont corrode. If you want a delrin can go ahead, they are lighter. But that doesnt necessarily make them "better"
I should preface this by saying I cut plastics and metals of all kinds for a living and I am just being nitpicky about "rust" WRT aluminum; it is a pet peeve of mine.
Since we started down the rabbit hole, after it is dinged or scratched oxidization can occur, plastic is homogeneous and doesn't have that problem. I hope the JJ and the Meg are type 3 hard ano which would help.
I am not really advocating for anyone material or another, there are trade-offs to all of them.
Why would someone prefer plastic to metal toys.
See above about trade-offs.
Also, there are some pretty bad ass plastics out there these days, don't dismiss them.
I am going to stop derailing this thread now on the materials tangent.