I used Quiksteel too but not on a kettle. Used it on a motorcycle exhaust w/ limited success. It's a liquid metal slurry that you have to mix first and then apply. The first application held for a bit and when I went to reapply some, I found the remaining Quiksteel had dried up in the container. So if you buy it, use it quickly as shelf life is only a few months.
Oh and Argent, I don't know about the JB Weld but the Quiksteel can be sanded, drilled, painted, etc.