My boat is a twin and had dual function controls on the flybridge when I bought it. It also had them at the lower helm -- but they were disconnected. According to a prior owner, they had never been connected, but I figure the first owner must have disconnected them for some reason.
I (re)connected the lower station using the seastar system with station selector. At the expense of needing to rotate a lever to switch between upper and lower, this choice eliminated any possibility of a miscalibration between upper and lower w.r.t. gear selection.
The installation took two afternoons and works beautifully. It went particularly easily because I didnt need to change the cables coming down from the flybridge. I just moved them to the seastar units and ran new cables from the lower controls and selector to those units, and then from those units to the engines and transmissions.
I basically use the lower helm to bump the engines while docking. While in Califonia in my old boat, I used to use it for night, fog, and bad weather operation in open, deep, and quiet waters -- but havent had that use case in Florida.
I can take some pictures and post next time I'm at the boat and answer any questions about the system installation.