If I may say, I like the split download better than the one apk with additional file. It's easier, simpler, and for those who want to save memory in their phone, it allows them to choose which part they want to install.
Though that's just my personal opinion.
It's also great to have everything in one app, but the benefits of split download I mentioned outweigh that.
I hope I didn't speak out of turn here.
Let me know if I did 🙂