Nice find on the Tsunamis! With short boats like that, you'll be able to get into a lot of nice secluded places, small creeks and hidden ponds.
Anyway, about the rudder...with that said...the boats are pretty short so turning wont be much of an issue. With one or two sweeping strokes, you can spin those boats right around.
And, if you don't have the experience already, you'll soon learn how to keep the boat tracking straight as an arrow without the need for a rudder.
Also, adding a rudder system just adds weight and its just another accessory you have to deal with if repairs are needed. Installation can be a pain in the "you-know-what" too.
I say 99.9% of the time you will not need the rudder. That 0.1% would be the day you decide to go out paddling on open water with a steady 25 mph wind. You'll develop much better paddling skills without a rudder.
rudder = crutch.
Good luck. Enjoy.