I have one. Use it a lot when I can. My Doctor didn't recommend it but when I mentioned it he said it wouldn't hurt and could help. For me it was a big help.

My board is good for 350 lbs and wasn't too expensive. Approx $200 a few years back.

It needs to be adjustable for your height and I prefer the locking pin as opposed to the strap to limit rotation.

Start small at 15 to 20 degrees and move up over time to where you think it is comfortable. I can do full 90 degree inversion and drink a bottle of water while playing games on my cell phone. The wife thinks I am weird. I think hangin upside down drinking at keg parties was good training. Who says all those crazy days were wasted time.

After you hang for a while and are ready to get up put the board at a level position and lay there for a while. It kinda lets your body relax with the stretch. I will often get off the board and take a nap to keep the load off my back for a bit and it helps the effect last longer.

I can't do sit ups because of the pressure it puts on my spine but I can do crunches while hanging upside down.