Ocusync, or at least my understanding of it, uses both 5.8 GHz and 2.4 Ghz, choosing a channel to use and switching between bands depending on which is best at the time. Keep in mind that radio signals as a bit like a flashlight, if the drone is behind an obstacle and cannot receive a direct signal, then an indirect signal that reflects of something else will do just fine. Different frequencies reflect and/or penetrate differently, so Ocusync's ability is key to improving comm between controller and drone.
A true Yagi antenna has a driven element, with one side of that element connected to the coax center conductor and the other side connected to shield. The back element is the reflector and the front elements are directors. The Yagi is tuned to one frequency band only, so in this case it will no doubt be 5.8 Gigs for that antenna's smaller physical size.. The slip on (over the controller's what I suspect is a 1/4 wave phased antenna array), is a "faux Yagi", as the driven element is a compromise. It may offer a performance gain, but I don't think as much as a real Yagi. In either case, the directional concerns, mentioned in previous posts, may also be a problem.
In the US, with our higher power FCC mode, I don't see a real advantage. In the EU mode, maybe.