How effective is this product on brass?

That's what I bought it for. Removing a brass bolt with a stripped head. Worked right away with little effort

I would check with you local Lowe's store refund policy on this item, should it not work. According to the manufacturer, this is made of high carbon steel which in a more dense material than brass and could possibly round it more. Before using the socket (should you actually buy it) I would take care to make sure that you've used plenty of penetrating fluid. If that doesn't work, try to safely heat the fitting where the threads are. For this job, I would recommend more of a drill-type extraction tool than a socket, since this is more designed for hex nuts and bolts. I'm not sure if it would grip properly.

I tried to use this to remove a hex bolt from my motorcycle. No luck. It wouldn't even penetrate the head. If it's an industrial type bolt or screw, I don't think it will work. I returned it as it was useless for me. Maybe it would work on household acres and bolts.

Yes, the Irwin 5-Piece bolt grip set is designed to grip bolts and nuts that are rounded off or painted over.