Save yourself tons of money and make your own back massager! I was taught this trick by a physio-therapist.
All you need to make this back massager is:
a long sock (your dryer may provide you one without a partner. lol)
a rubber/tennis ball
and now simply place the ball into the sock. I got the ball at a dollar store and used an old partnerless sock we had.
Sling the ball over your shoulder and position it where you need to massage.
Stand against the wall with the ball between your back and the wall. Now simply press the ball against the wall and move up and down and around to massage out the kinks. Just move the ball all over wherever you need it. You can sling over your shoulders or place from your side, whatever works best to reach your problem area.
This massage technique works great for people with Fibromyalgia.