I've considered a tank but the well is "set up" without. I was told by the well installer that it was "ready" for the connection of wire from the controller to the well. I'm not exactly sure how this works. If I go with a tank, how does the well pump know when to turn on/off?
It sounds like a pump control relay is already wired in, if it requires only a direct connection to a controller.
The advantage of tank/pressure-switch control is independence of operation. If some fault shuts off a zone, even while the controller 'thinks' it's watering, the pressure switch will shut off the pump. With relay control, nothing will tell the pump to stop trying to push water into a closed system, a phenomenon called "dead-heading." Relay control requires you to depend on a pressure relief valve to open up and spew water, in order to avoid dead-heading.