Jean,
Which tank would you prefer, if you had to replace a crash damaged Roadster tank. Steel, aluminum, fiberglass or one of the gee whiz plastics? I don't even know if there are any plastic tanks available in the Roadster style.
When I replaced my glass Roadster tank, which had not yet developed a leak, but the experiences of others here with lining tanks prompted me to replace it, I chose aluminum over the other materials. I'm not familiar with the plastics. That left steel and aluminum. I was aware of the rusting problems with steel and I wanted to stay away from coating of any kind. I'll admit, I kind of assumed aluminum was impervious to ethanol. From what research I've done, it seems the problems with the aluminum motorcycle tanks are pretty much negated by frequent riding or if not riding, draining the tank. I sometimes do wish I had a steel tank so I could use my Marsee magnetic tank bag.