I like this product. The delivery was excellent and the armband is fit for purpose. A couple of slight criticisms...
As pointed out in other reviews, the strap isn't quite tight enough for me. I imagine this could easily be rectified with a little modification on my part, but something to consider if you have smaller arms.
Also, due to the fact that the phone is slotted into the case through a wide opening, it means that you can only wear the armband one way up and, since there is no hole at the bottom of the case for earphones, it means you can't wear the armband upside down on your arm. Not something that bothers me, but a lot of people seem to find their phones easier to view when placed upside down on their arm. The fit is nice and secure and the phone is in no danger of popping out.
The armband is quite bulky, but the iphone is not a small device so I don't imagine it's any bigger than any other product on the market. It also has a handy little key pocket, which is nice.