If I may chime in, I make my living driving ribs as a sailing coach and I can not imagine not having a steering knob; I always bring a spare on the road with me and install it on any rib I charter.
I'm on a rib solo 95% of the time. I consider it a safety feature as I am able steer the boat safely with one hand at slow speeds allowing one free hand to hold on to a ropes (buoy), the throttle or fiddle with something while moving.
Parallel parking a rib is a breeze with a steering knob.
In the States, a company called Edson sells the best one I've used, they are not cheap by any means but they are excellent with sealed ball bearings giving no play/wear and super smooth, the knob itself appears to be milled. All stainless and never had one jam up or rust out, extremely solid feel. Highly recommend. FYI: I have no connection with this company.
I've also used many times with good results when I'm in a pinch is the cheap ones available at auto stores. The one pictured below is my preferred one, yes it has some play and can feel chintzy but they work but can't say for how long as I usually use that rib charter for 10 days up to 2 months. I just leave the knob on the that rib and buy a new one for each charter. I'm always afraid that one may break but in the last 10 years none have broke.
I do not like using knobs that are not on the same axis as the steering wheel for three reasons. The boat builder chose a certain diameter for that boat for the correct feel and peformace for that boat; second when knobs are mounted on the outside of existing wheel it can interfere with the clearance around the wheel giving your hand more chance of hitting something like the throttle or other items near the steering wheel. They are also more prone to slip/come loose/move while operating.
Link, I'm sure you can find the same one cheaper: