Unfortunately, I have not played with the USD FF yet so all my comments are based on what I saw in the published material and their website.
The Okii USB controller
Easy to use and setup (once you learn how to use it). No need to setup the camera on rails and put gears on the lenses. This is a big plus!
The controller does not just control the focus, it can be used to control many other camera settings without having to touch the camera which is a must when doing remote shooting. This is so useful!
Since this is an USB product, range is limited to a few feet. It is unclear if it would work with USB extenders/chained hubs.
While marks on a focus disk are good, having the controller store the exact position of the various focus point is even better.
What about the Jag35 EFF then?
It can send its signal over a much longer range than what is possible with an USB cable.
The Jag35 EFF can change the zoom range of the lens, not only the focus. This is not something I see myself doing often, unless the camera is set in a remote location and I have two motors: one of the zoom wheel and another for the focus. Still, it is possible.
Rack Focus speed control
The Jag35 EFF gives you total control over the speed at which the focus should change. This is a blessing and a curse since it means someone has to be in charge for rotating the focus wheel at a constant speed.
To me, it is clear the USB FF Controller has the upper hand. The only people who should go with the Jag35 EFF are those who need range, zoom control or don’t like having a controller telling them at which speed the focus should move.
If anyone is interested, I would gladly trade my Jag35 EFF for one of these!