First of all, there is nothing wrong with this holder, it's purpose built for the S4 and looks and feels great. However, I like to have a back silicon cover on my phone so as a result my phone does not fit in this holder.
So the options are simple, if you are like me and prefer to have a back silicon cover - then this is not for you.
If you don't have a back cover then I would throughly recomend this.
Because there is nothing wrong with this, I will not be asking for refund - I'll get my money back at a car boot.
Hope this is helpful,