It would be accepted anywhere coupons are accepted, you do want to check with the stores coupon policy, once in a while you will come across a store that accepts coupons but does not allow Free items.
Does it have to be Refreshing Mango specifically? The coupons in the picture just state that it has to be the Coconut Water line (unless it's in the fine print).
Yes it lists Refreshing Mango specifically. I have purchased a different one in the Coconut Water line at Walmart, I am not sure if it was something that is normally done but the cashier did not say anything.