bottom feeders are supposed to take the mess out of dripping into an atty... for those that don't like to use cartomizers, although some use carto's on their bottom feeders.
a bottom feeder pushes juice up a tube into the bottom part of the atomizer or cartomizer by squeezing the side of the bottle.
the downside imo is that you can over feed and get flooding, leaking and gurgling, but you just need to learn how to squeeze properly.
the Provari is a regulated variable power tube PV... it is not a feeder. You have to either drip an atomizer, use a cartomizer or a tank system... it has LED readouts for voltage control 3.3 to 5.9v, regulated (boost) to give constant voltage without drops due to battery discharge cycle, battery check, power on/off, and checks resistance of the atomizer/carto/tank mod.
two very different PV's... btw some bottom feeders are VV variable voltage.