I bought a couple of these to keep my shoulders in shape for baseball.  They're pretty tough and last a while.  I've had mine for over 2 years now and I use them at least 3 times a week.  I also keep one in my baseball bag to warm up before throwing, so with the dust and abuse, it is still holding up fine.  The door attachment can harm your wooden door if you place it wrong, however, I don't even use it; most of the time I just hook the handles together through a stable beam or something.