Yes, that's the one. CLICK HERE to see how you'd set up a Sidekick on any arca-swiss compatible head. You attach it as shown on that site and just loosen the "panning" knob so that you can pan side to side (using your ballhead's panning feature) and can also pivot up and down (using the Sidekick) at the same time.
However, I missed the part where you already have the Opteka. If you like that, it might be worth keeping. The Sidekick/ballhead combo should work pretty similarly. Not sure of the quality difference, I've never owned a true gimbal style mount, I've only had the Sidekick/ballhead combo.
I don't have a Sidekick right now (gave up birding for the last couple of years), so I was planning to get something like the Opteka if I buy the Tamron and am not happy with hand-holding and monopod attachment. I'd prefer to NOT buy a gimbal/sidekick because, when I had one, I rarely used it due to the inconvenience factor. I did, however, heavily use the Sidekick for a couple of trips to shoot Bald Eagles at LD14 in Iowa where it helped immensely. Of course, I was able to set up my tripod within 25 yards of my car since the BE's fly so closely to that location, haha!