Actually using tiny slices of circle being rendered with Sprites is the way to go as you get maximum performance and a very smooth app. If you drew the pixels manually, your app would have different performance metrics depending on the device you are running on. It is always 1000% preferred to prepare your graphics in advance and find nifty ways to render them as finite elements (if you want performance). We are looking at some cool 'image generation' commands for AppGameKit, but even with them integrated, I would still recommend the old 'prepare assets before loop - prepare nothing inside loop' approach.
I drink tea, and in my spare time I write software.