On a tripod over a metal roof should work fine; however be aware this is a Chinese knock-off of a Comet CHA-250B:
Jetstream isn't a manufacturer, they're an importer/distributor of products from China. The original Comet CHA-250B is made in Japan and the Jetstream is a "knock-off" of that. I'd be mostly concerned about build quality and also whether the tripod is strong enough to support a 24' long vertical antenna in a strong wind, as the forces on the base and mount can be amazing.
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