It looks like I was wrong: the macOS version has lots of Swift frameworks inside of it and no hints of Xamarin, they appear to be two completely separate apps
I'd prefer something like Fork over something like GitKraken IMHO. I cannot imagine the performance of some electron alternatives if I were to open a repository with 200k commits, but this can be resolved with shallow cloning.
Even if it has lots of Swift frameworks embedded, as soon as they switch to Swift 5 and Mojave and higher, Swift will become built in with no dylibs.
I'm curious why they didn't use Xamarin.Mac though, they could have shared a lot of code between apps.