For Apple and not for the consumer.
Basically the iPhone is like DSLRs these days. Once you have one there's really no reason to upgrade generationally because they're THAT good. So what can Apple do? Well, sell you something for your iPhone.
So, it solves a problem for Apple. What critical-path problem does it solve for consumers? Well, you don't have to fish your phone from your pocket to see who's calling. That's a bit of an issue for those of us who live where we have winter but it's not a really, really do-or-die feature. So, really it's following the delude-yourself-into-thinking-this-will-make-you-lose-weight item like 99 per cent of the sports equipment out there.
Look, you'll either go running or you won't. You'll either play sports or you won't. It's a bit like saying you'd take up drawing if you had the right pencil.
I've not doubt that Apple will sell a lot of them but really it's a solution in search of a problem for consumers.