Naval Jelly isn't a rust inhibitor, it's a rust converter, and I don't believe you're supposed to leave it on. I think you're supposed to treat it and then remove it. I'd classify it as good for surface rust that you want to stop rusting and you plan to paint/coat. And with POR15, you need to clean and prep before you apply, because it cures and encapsulates the rust. I'd say it's a good permanent fix if you prep properly, like an axle housing, but it's also harder to remove than paint etc. if you're doing additional work in the future. It's also UV-reactive.
Your best bet if you want to slow the progress of rust and you're going to have it repaired eventually is a true inhibitor, such as an oil-based product. My favorite is Fluid Film, I've put it on older cars where there's surface rust that I don't have time to address, and it seems to drastically slow the rusting process. (I'd say it "stops it", but rust never sleeps...) It's also good for undercoating prior to winter. If it wears off, you just add more. Easy to remove later too.