As a single traveller, I can't just leave money, cards, phone etc with someone else whilst I take a dip in the pool, hence I bought this product. Well, it worked a treat, not once did it leak, and it held everything I needed it to. I never tried to use my mobile phone whilst in the pack, but to be fair I was on holiday, the phone was for emergencies only - in which case I'd get out of the pool anyway!
My only gripe, and the only reason this is not getting 5 stars, is that it can be very fiddly to open when you have wet fingers. Double edged sword though I guess, because if it was too easy then there's more chance of things getting wet.
Overall, I would not hesitate in recommending this product.