The fact of the matter is, wearing one as a reminder helps a lot of people push over the edge and is partial motivation to do more than you normally would. The monetary investment means you will commit yourself and defend the purchase more. The visual reminder will make you set small goals to go along with bigger goals. One of those things where you wont know what you're going to do with it, until you experience it firsthand.
They aren't all that accurate though, which is why the trend on these is everywhere. No fitness tracker/smartwatch on the market is highly accurate. Which is expected, the sensors haven't changed much in 15 years.
So really, if you're the kind of person who knows deep down they wont ignore any form of fitness tracking device, you'll be better than without. If you know you'll wind up blowing it off, then keep searching. I had a misfit shine just because it didn't look as douchey like a guy wearing a womens hairband or those stupid livestrong bracelets. It was a fun toy before it got old, but it still works as a watch. The options are even better now.