I have a 6 way seat in my Challenger and while it is a nice option, I cannot say I would go out of my way for one, kind a PIA to use. I had to really go through mine to get it to work correctly because there are gears in the back and over time they get pretty hammered and don't like to work well. Not overly complicated to fix or make work but does take some effort.
Yes, someone does make the the knobs, I bought some a few year back but I don't remember from who, Tony's parts maybe.
The 6 ways I believe are
forward
backward
tilt front
tilt back
up
down
I might be off on those, I would have to go out and sit in it again
I've figured out that the rectangular handle also moves forward, but not what that does.... I'll keep experimenting!
Edit, It is for up/down... I guess it could be useful if you're under 5'-6''...
Ben