I took mine back to the store I bought it from, they replaced it free of charge, (keep your receipt) I had the ms band 2 only ten days, I go to the gym every day, that is why I bought it. The screen developed a crack, but ms wanted ?133 to exchange it. They stated cracked screen is not covered by the warranty.
This is not entirely true, in the UK when you buy an item, it must be suitable for its intended purpose, under these conditions you are entitled to a replacement or repair. I got it replaced no quibble, you can also request a refund, but I opted for a replacement.
MS is under no obligation to provide you with anything, especially as they provide the warranty, however you have additional rights as a consumer with regards to the product and its durability. This varies by country, but basically it should meet a certain standard. judging by the reports, its not as durable as it should be for a fitness product, therefore you can exercise these rights and should use them.
I took the extended insurance out after they replaced it, as one year wont be enough piece of mind for this item. Considering what we paid for the band 2, I am appalled at Microsoft attempting to rip off consumers in this way.