Your cello stool looks like a fine product. One additional feature that possibly could be attractive to certain cellists is a slight forward tilt. I had a teacher who had his cello chair built this way - front legs a bit shorter than the rear ones. I use a standard chair but put the back legs on pieces of 2x4 to raise the back and give it that tilt. If you were to slightly angle the cut on the bottom of the sides of one stool to give it this tilt, you could let cellists try it and see if they liked it. Just a thought.
I agree with robcat that the height adjustment mechanism looks a bit labor intensive, but then once it's adjusted, it shouldn't need further adjustment very often.
Best of luck with this product.