I have one and I adore it, but it also depends if you are competitive towards yourself. I push myself to beat my own personal records but beside that it also just makes you aware if you excise enough every day.
Meh. Phones have so many cool apps for stuff like that nowadays.
True, but if you work in a shop or do a job where phones aren't allowed during work time, a device like Fitbit comes in handy to track, because loads of jobs do allow a 'watch'.
Only if you are a detailed person and like comparing charts. Otherwise it's useless.
So if you get off by walking 20 more steps than yesterday get it. If you feel bummed cause you only burned 500 calories and want to make a goal of 550 tomorrow get it.
Otherwise phones have decent tracking apps, but aren't 100% accurate.