Depending how you run your cords, they can control many more than that.
Herp 2 has 2 outputs, but it will also run a certain watt per output. Ie, more than one heat source. I have a 2 and run 3 racks off one output and my incubator or room heater off the other. Ive heard of ppl controlling entire rooms off a herp 4 with multiple full sized racks, incubators, hatchling racks and room temps. Probe extensions are also available.
A 350 dollar multiple output thermostat will pay for itself in its flexibility in no time. And depending on your projected size, may very well only ever need the one, with a possible back up