I saw this shape when I was out running; it was about 3 feet tall, made from concrete, and used as a planter. I liked the shape and realized that it had a fairly simple design: the bottom was circular, and the top was a square with filleted corners.

When I got home I found I needed only 4 curves to reproduce the shape: a circle at the bottom, t squares with filleted corners near the top, and about 1/3 up from the bottom a "tween" curve that is formed by making a curve that is literally in between the circle and the filleted square. I used these 4 cures as control curves for a Loft surface, and that was it.

This part printed in a little less than 15 hours using a layer height of 2.03 mm and print speed of 100 mm/sec. But be aware this was because I used a new type of infill called "lightening" that is now available in PrusaSlicer Ver, 2.5.0 Alpha 3. This infill only adds infill where it is absolutely needed, which in this case is right near the top of the print. There is nothing in between the inner and outer walls of the print. The estimated print time for this print with regular infill (15% triangles in my case) is just under 20 1/2 hours. So, as the saying goes, "you pays your money and takes your choice."