Being a woodworker, I would like to point out that a three-legged stool is always stable, no matter the surface it sets on. It is always the fourlegged, or more table, stool or chair that wobbles, and occasionally needs a match book or other shimming to sit properly.
The editor intimates incorrectly that it would be difficult and undesirable to build a three legged stool.
Hopefully you will reassess and clarify your evaluation.
Having had three legged stools, though, I'd tell you that the are stable in theory, not so stable in fact.