For anyone thinking this is the solution, it's not. This technique produces a rasterized circle in a destructive editing workflow. What people that are complaining actually want, is a non-destructive tool, like the planned shape tool that will let everyone easily make vector shapes, like circles. It is part of the ongoing plan to add non-destructive workflows to GIMP, it's a game changer and the gimp team is doing great progress, so kudos to them.