I had one. It does work. My issue was main upper back and it didn't work as well for that, but it does give a good decompression to your lower back. I considered getting an old motorcycle helmet and possibly weighting it, but I never did.
There are other methods that would likely have a similar results without having to have all the blood flow to your brain.
The vast majority of people with low back pain have tight hamstrings that either cause the problem or make it worse. I know people that have "cured" their back pain by properly stretching their hamstring on a daily basis. Most people don't believe the problem could be that simple but it's worked for about 5 people that took my suggestion to do it.
You probably need these: