The iPhone footage looks best to me in that video. Which begs this debate... (and this is totally subjective). To me, videos I take with my iPhone 6s Plus look better than videos I take with my P3P and better than what I've seen using an Osmo (no, my iPhone can't take aerials, and I don't have a gimbal for my iPhone).
That being said, rather than getting an Osmo, why not just get a nice motorized gimbal that holds an iPhone? Something like this:
iStabilizer Gimbal - Smartphone Video Stabilizer – iStabilizer
(there are cheaper ones)