I had bought them off of ebay from SHO, Whatwears, etc. They were inexpensive, so I just went for it without really researching. The material is not made to stretch, and the binder goes around the back as well (which it shouldn't unless made to correct back posture). I have heard of someone getting one of their ribs pushed inwards after wearing a binder from one of these brands for a very short period of time. I have also had a bit of difficulty breathing and experienced sharp pains in my torso while wearing them.
I plan on buying a compression shirt in the future, but I may have to stick with the sports bra method. I used to take two sports bras and put one on properly, the other on backwards. It will have to do for now, I suppose.