One reason why I`ve passed on The Bone is that it looks like it`d hold/retain water and I spray a lot of water/etc. when working on the undercarriages. And while the padding on my creepers isn`t anything great, it`s better than hard plastic. AND..gee, I`m really slamming that thing

...it looks like it`d be harder to get on/off of than my regular ones (noting that I`m, uhmm..pretty agile for my age and get up/down a lot quicker than many, dozens of times per wash) and harder to grab hold of to move it around (no framework to grab).
I`m using two old Griot`s creepers...one a plain flat one from right around the time Richard founded `em and the other is the first of their fancier Cadillac of Creepers with an adjustable headrest...which was always slipping out of position often with head-banging effect. I finally removed the tilt mechanism and fixed the headrest in place at a kinda-OK angle.
They are in *terrible* condition...but are really easy for me to use since I have decades of experience with `em; know exactly how much pressure I can put on which part of `em to avoid any tipping/etc. and they`re both really easy to grab hold of and more around. When I`m gonna be up/down so many times I don`t want to make it hard on myself.
AND I bet that what I like wouldn`t suit some people any more than their faves would suit me!
I too use my round-cushion, height-adjustable seat the most. Got mine from Imparts back in the mid `80s and it`s still fine though its padding is pretty broken down.
My flat seat one came from Griot`s, but other than having a drawer (which I basically never use) it`s just like the Detail King one.
Gee, I don`t use either of those seats for months at a time.