I have one that I bought from Relax the Back. I love it!
When things are REALLY bad, it does not make a huge difference. But, when I am in the middle, I can feel nerves release as I tip upside down and compress again when I go right side up. Not sure of long term effects, but short term effects make it worth the $ for me.
I also have a Zero Gravity Recliner from Relax the Back. I can feel the same effect when I sit in the chair. It is great for naps, too.
(and no, I don't work there)