Not to throw them under the bus, but ADATA is a pretty budget-oriented brand. I say that because our boss purchased several new iBuyPower desktops and within several months, one of them had a RAM DIMM fail! And it was indeed an ADATA module. That's not to say that you have any more or less chance of failure with other brands, but I believe the quality control is better at, say, Crucial, or Corsair.
If one of them is bad you could RMA it... or even return it for a refund if possible (usually I think with RAM it is not but that all depends on the vendor). I would actually bite the bullet and order a pair of 8GB DIMMS so you have 16GB total. Being a new computer and all, there is a pretty solid chance you are going to hit the wall pretty quickly with just 8GB available, during the "lifetime" of your new PC.
If your idea was to add two more 8GB DIMMS later, I would do some research on fully populating your RAM slots as I've heard that it can actually decrease reliability/performance.