Day One 2 is out. I think it's a well rounded app although my first experience wasn't completely smooth. Still worth buying.
After a quick think, being happy with Day One Classic, I bought it assuming that the previous version won't be maintained for much longer even though I'm a very light user.
Everything imported well and quickly. The previous version synced to iCloud but now you must create an account and sync through that. This isn't explained in the interface so I was tapping on the sync preference wondering why no options popped up. Until you sign in it is unable to sync.
The app asks for your location permissions even when not using the app. This is a pet peeve of mine because I'm aware of the additional power consumption this brings. In addition I don't like being followed. When declined any feature that depends on location is still enabled but just won't do anything when tapped. Going into the system settings reveals a third preferred option of only using location when using the app. I prefer being in control of things like this.
Day One doesn't explain what is new in the app although it is instantly apparent that you can have multiple journals. Not sure why I would want this though, because I'm mostly using it to record how long ago it's been since certain events happened (light user).
Conclusion
It's clear this is a premium iOS app and all of the above niggles can be easily addressed. I have removed the classic version as a sign of confidence.