Well, at least that one being sold by NRAstore is running cheaper than other brands now and seems to be a much better deal. The one I have I bought for $15, but now it is going at $35.00.
Your link from the NRAstore appears to show the band as being more sturdily made. The stretch enables your gun to be hugged closely towards your body, providing for better concealment. I'll have to look at this one to compare. I do need a new one to replace my old one... However, I have my eye on a different brand that will allow me to carry two firearms.
In answer to your question whether you can wear without a shirt under it... sure you can wear one without. I will say, however, having a shirt under does aid in providing more comfort.