As already noted, they are only slightly less noisy, but lower in pitch (tone) than stock props. I'm not the best one for testing as I don't find much time to fly just now (retiring soon). Couldn't resist trying these and I'll carry them with me. As others have said, the folding props stay on in the case, these don't. But whenever I'm out where there might be people, I'll put them on. I love how the Spark is so inconspicuous.