I like the idea and the overall design but on the 'Log' page the top circles are a little confusing. I was trying to tap on them initially and it took me a few minutes to realize that they just showed the status. If they were different then the rest in some way it might make it more obvious.
I would also love Fitbit integration. I know a lot of people who have them (myself included) and because I would still have to use two apps might prevent me from using Nudge long term.