There's really no way you can speak for even more than few other people, let alone most or even just 50% of people. It's rather silly to assumer otherwise. And if it's not hard to show, it would have already been shown by now--simply saying it or thinking that's the case isn't showing it, and since there's no way to speak for even 50% of people out there, there's really no way to even show it. Sure, lots of assumptions can be made and all that, but that's not really showing either.Most means the majority of people, meaning over 50%. I was being generous here, so that I wouldn't shoot myself in the foot. Its not hard to show that it'll be useless the majority of people. It's probably more accurate to say this watch is useless for almost everyone but that'll be hard to prove so I won't say that.
And by the way, most isn't majority, most carries the implication of much more than just over 50% (the use of most would would generally be considered to be much closer to 100% than to 50%).