First time seeing this thread, but I have to chime in...
Thinking it was a marvelous idea, I bought one of those 'folding' creepers that you lift up part of it to create a rolling stool.
It's been in the cabinet for a few years now, and I hadn't used it all that much as a stool until a few weeks ago when I was removing the front bumper to clean and paint it.
Let's just say that my current stature proved to be too much for the poor thing, as when I sat upon it for the last time, the stool shifted, which made it roll a bit, placing all of my weight on the wrong side of things.
This bent the "heavy duty" frame and launched the stool out from under me across the floor while causing me to land as awkwardly as possible with my ass/lower back firmly along that concrete step that you can see in my profile pic.
I'm no sissy, but the way I landed was excruciating. I laid there for a few minutes writhing in pain and gasping for air, hoping on one hand that my wife would come by to help while on the other hand hoping that nobody would find me in such a state. It hurt so badly that I fully expected to piss blood.
I hurt for about 4-5 days, as much as if I had been in a car accident. The bruise to my ego was only outmatched by the one across my backside.
All that said, I have a barely (albeit harshly) used creeper for sale through my local Offerup account.
I'll be taking the aforementioned recommendations to heart before I blindly purchase another of Mengele's creations.