Just to expand on the “behavior” bit, there’s a truckload of little things that native AppKit apps get you that nothing else will, not even other “native” toolkits like Qt. Things like Option-clicking a disclosure triangle in a nested list expanding/collapsing all children recursively, which one comes to use frequently and misses when absent. Foreign toolkits have spotty coverage of that kind of thing if they implement any at all.

As much as visually fitting in is important, behavior is perhaps bigger. Anybody who’s working on the Mac port of a cross platform toolkit would do well to replicate those little bits.

I find the sqlitebrowser UI to be perfectly fine. It's not pretty, but it's a tool so who cares.