In particular on the Mossburg 835's, do they make a difference? Pros and cons...

I would say if you closed your eyes and could shoot 2 835's with one barrel ported and the other one not ported with heavy turkey loads and could consistently tell the ported barrel vs the non ported barrel as for less kick you would be very lucky.

They are louder and reduce kick and muzzle jump very little.
To me it does not matter either way if my barrel is ported or not. It would neither influence me to purchase a shotgun or keep me from purchasing one.