No... you can use carts, but at higher voltages the carts will dry out faster, and you should take care to keep them wet. Folks that use the SD with carts top off regularly with an occasional drop on the atomizer. It should be the same with the Prodigy at 3.7v.
At 6v, I imagine you'll just want to drip to make sure the atomizer stays wet.
Thanks Walrus, for the info. Dang, I love my coffee filters.