I agree with you Geoffers.
My company SOPS's are that on coasting out we arm the floats. I do this. The SOP's of my previous company was that floats were armed below 80 kts. I did this too.
My company SOP's are that the AP's are disengaged on the ground. I do this. The SOP's of my previous company were that the AP's were never disengaged. I did this too.
My company SOP's require brakes to be applied before landing offshore. I do this. The SOP's of my previous company were that brakes were only applied after landing. I did this too.
Like you I find it irritating that people decide their own SOPS's and every time I fly with a different pilot I seem to end up debating the merits of different actions.
In any incident or accident you will be asked why you did not follow company SOP's. If you didn't you will be at fault. If they differ from the manufacturers SOP's then the company are at fault.
And I don't forget to arm floats, disengage AP's or apply brakes because I follow the checklist of whatever company I am flying for.