We have 3m. I agree with Multihullsailor6 on the whole.
I would add that we rarely use the fixing points. This is why.
stern to a floating pontoon they are normally low enough that you can just step over from transom to the pontoon. So the passerelle only really comes useful on a concrete quay where the height means that you want to step from a higher (and further) step to the quay. Now, if the passerelle is fixed into its fitting, the angle between its base and quay becomes important. Too steep and the quay end of the passerelle is in the air and dangerous. 2 fittings is an idea but you might not want to have a fitting on the engine
cover as they can leak, or you have to remove the passerelle to access the engine
So that is why we rarely use the fitting, but, instead simply secure the end of the passerelle to whichever step we use, making sure the boat end of the passerelle is sitting on a foam pad.
I agree longer is better. Either have wheels on the quay end or run lines to the boom/mast to stop it dragging on the quay as you move around. Weight is really important (we have aluminium, but I am seriously considering going carbon. We never use the handrails. It makes it feel narrower, wouldn't hold the weight of a person and is a faff. Personal opinion though...
Remember to measure your hatches to make sure you can store it.
Nothing wrong with a plank, but if appearance is important an old bit of wood
might let the side down a bit...