I suspect the UP will outsell the FitBit by at least an order of magnitude, if not more. I'm not saying it's deserving, but they just seem to have a better command of all the buttons to push (marketing, presentation, lifestyle, etc..)

Wearing a bracelet is a lor more intuitive and part of established customs. This is a plus for UP. It doesn't hurt too that people over the past 5+ years have been going nuts on all kinds of rubber bracelets. Sure, there are people who don't like wearing adornments, but they're in the minority camp. I'm sure the technology could quite easily be wrapped into any shape, as long as the software is updated to properly deal with the new data. In this case being distinctly different than everyone else is a huge advantage.

Does the FitBit talk wirelessly to a phone or only to a computer? If only a computer, that's a huge negative, even though it's wireless. Society is moving away from the computer as the hub. A lot of people have only computers that belong to work, so their only "personal" computing device may be a tablet or phone. I have a lot of friends in the corporate world like this.

The iOS requirement for the UP is temporary, but not in the least a problem, since iOS consumers account for the majority of persons who would likely buy such a device in the first place. If you have limited engineering capacity, develop for the widest audience possible first. Android support is coming.

You can go swimming with the UP device. You don't need additional attachments to put it on your wrist when you go to sleep like the FitBit. If you're already wearing it, chances are you'll keep wearing it. If it's just another little device, chances are you'll stop using it.