I would have those same questions DNJ, although it is a neat concept for certain situations.
I have used a drafting stool for many years. Totally adjustable in height, and it has rollers so I often use it for a dolly. I seldom take the Rock n' Roller unless I have a long way to transport things. It takes more time to take the dolly and gear out of the van, load it up, wheel it inside, etc., then find a place to park it while I work than it does to make a couple of trips. I need the exercise anyway, and none of my gear weighs more than 25 pounds.
Of course at the place where I work most of the time, I just pull up and there are several guys rushing to see who gets to carry my stuff in. A $5.00 bill still goes a long way!
If that seat had rollers and was adjustable in height, I would be interested because I would just leave it there, even when I'm not going to be there for a night or two. I could stash stuff in it that I only use there, such as small lights.
It's really expensive though!