jjrbus,
I've used the silver/aluminum faced version on several houses with excellent results. My Home Depot didn't carry the white. The last time was 3 years ago to seal a horizontal lap joint in steel/aluminum at the top of a boxed in manufactured chimney. No leaks so far. I was up there this summer for another purpose and all looked fine.
At that same job I slid sideways a bit into a handrail. The result was a small crack or puncture in my fiberglass siding about the size of a matchbook. I cleaned the area with MEK or acetone and applied a "temporary" patch. Yep, it is still there.
I hate to post anything but questions here as I don't have my toy box yet. But I have used the product - unlike the naysaying experts on camping world's forums.
fleamarketeer