Good question. I did have both Zeo and Fitbit on for a few nights. The comparison is a bit apples-oranges. FitBit tells me:
1. Time I went to sleep
2. Time to fall asleep
3. Total time in bed
4. Actual sleep time
5. Times Awakened

Zeo told me times in Wake, REM, Light, Deep sleep. The only common metric was number of times awakened. Since I have a 2 year old, I get up 5-10 times per night on average. What I found was that there were a bit more false positives on Fitbit (for times awakened). That makes sense since Fitbit relies on accelerometer, not EEG.

I couldn’t wrap my mind around how the different phases of my sleep mattered (e.g. does 45 minute deep sleep mean normal for someone like me?) Plus it was a chore to keep track of lifestyle factors and log them in Zeo to correlate with sleep quality. So I returned it. Since I don’t suffer from any sleep issues, Zeo was an overkill for me. I find FitBit more useful (esp. #2,4,5 metrics), even though it may score low on accuracy.