I have one, again mixed results.

Bought it when facing an RTW in Y while suffering severe back issues. Couldn't justify the extra $12K for J class so spent money on making myself as comfortable as possible.

Ended up only in Y for the SIN-FRA long flight, was upgraded on the rest of the long-hauls. So used it only once. Survived the flight, still able to walk but it was a rough night. The airline helpfully stowed my cane in the overhead (regs) so I had the devil of the time even standing up since my back was so sore.

This product, in no way, approximates the comfort of being upgraded.

Tried it in the car (for longish drives) and again didn't find it worked better than a selection of inflatables.

I now just travel with three inflatable pillows, one for lumbar, one under my leg for the sciatica and one for my neck. Combined, they are lighter and more flexible than the 1st Class Sleeper. But mainly I travel in business class.