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I've used them. They are a lot stronger than they'd seem. If you need a better insert get a Timesert but Helicoils should be good enough for everything else. I don't know how watertight they are, I'd bet they leak.
Anyway, just drill it out, tap it, screw in the coil with either the official expensive-ass tool or a small flathead screwdriver, and knock out the tab. Good as new. In fact, slightly stronger than new.