There are many grades of sphagnum moss and you always get exactly what you pay for...
The cheap stuff has its uses, but it is not going to last as long or be as 'fluffy' as a higher grade. It probably works as a component in mixes (chopped) or as a base layer in a vivarium. We use 5A moss for the really expensive orchids, and 3A for most of the rest. I don't think the cheap stuff gets anywhere close to 3A. Inexpensive moss also tends to have more sticks and debris.
Regardless of what grade you use, I recommend thoroughly hydrating it before use. If you don't get it wet enough, it just doesn't work right. I take a brick of moss and set it in a large water container (5 gallon bucket usually). Fill the bucket about half way with water and let the moss sit at least overnight. Dump out the remaining water, squeeze out most of the remainder from the moss, and 'fluff' the moss.