The seiza bench (seiza is a Japanese word for a kneeling position).
This bench is surprisingly comfortable! Everyone thinks “oh, it must really hurt the knees” but it doesn’t. Nearly all of the body’s weight is supported by the seat underneath the sub’s ass. There is very little strain or pressure on the knees… and even that little bit can be alleviated by knee-pads.
The biggest problem, like with most bondage chairs, is that the arms tend to fall asleep if they are bound too tightly behind the body.
The bench is good for 2-3 hours of play.
Oh, and the dick can be taped down nicely to the L-bracket between the legs. Doing that seems to make half of the guys hard… but unfortunately the other half go limp whenever that happens.