FWIW, I find Zen on macOS to have much less of that uncanny clunky foreign feel that Firefox and its brethren such as Thunderbird on macOS have never been able to shake. It’s no Camino[0], but it’s the closest thing I’ve seen since to a Gecko browser that feels like it actually belongs on macOS.
I’d rather see Orion continue to be developed alongside Zen though, because goodness knows we need more non-Chromium browsers.