My grandfather has one. I've tried it a few times and it's given me not much more than slight discomfort and a rush of blood to the head, although it's kind of fun to play on. My grandfather found it terribly uncomfortable at first, but thinks it's helping him with some pains he's been having.
My chiropractor has one too. He says he used to feel more energized after he's hung on it, but that recently, he hasn't noticed an effect.
The manufacturer has a few accessories, some included and some sold separately, some of which I found to be gimmicky, such as the "Acupressure Nodes & Lumbar Bridge". They seem to work off the idea that stubbing your toe will make you forget about your headache.
The contraption itself seems sturdy. The plastic tends to discolor white-ish when bent, like those kinds of plastics do, but doesn't feel like it's about to give way. Besides the plastic back rest (which does feel sturdy, but of lower quality), the rest of it seems to have a decently good build quality to it. The pivot points especially latch in quite securely, the welds seem well done, and overall, I feel some decent attention to quality went in to its construction.
If, like my grandfather, you're not the flexible type, I highly suggest tying a rope around the ankle clamp release thing. It works quite well if you don't flex well enough to reach near your ankles. I tied the other end to the square support bar that runs up the back so it would always be in reach (right about knee level).
Be prepared for other people, young and old, to become curious and want to try it. It'll be one of those "Oh, I've heard about those!" things for them.
Additionally, when you first set it up, make sure to have a second person nearby (to potentially rescue you) while you adjust the height of the foot/ankle support. Adjusting the height changes the balance. You'll want the board to go back upright when you lift your chest up slightly.
Is it for you? Maybe. As with anything, I recommend researching the subject before purchasing. (Or buy it on a whim like my grandfather did. I won't judge. :P)