My experience of the AA J seat last week was mixed, flying as a BA strike refugee.

While the seat is perfectly comfortable in the lounge recliner position, it is in my view a pretty awful bed: too narrow and way too much hard plastic intrusion against the arms. My experience was not helped by the defective arm rest that refused to lock down restricting the available width by almost 4 inches. Luckily, as my flight was not full I was able to relocate from 10J to 08J but encountered the same malfunction there. The arm rest in the empty 08H thankfully did collapse and lock combined with lifting the console arm upwards allowed me to sleep intermittently for a few hours.

The Lufty example is notably more comfortable in my experience.