If anyone is interested in further reading, I designed one of the smallest known Hall Thrusters while doing a research internship at Princeton University [1].
Abstract: Electric propulsion provides a significantly higher specific impulse that allows mass reduction for spacecraft when used in lieu of chemical propulsion. For micro and nano satellite applications, plasma thrusters should not only be miniaturized in mass and volume, but also capable of operating efficiently at very low power levels of a few watts or less. Research was conducted to determine theoretical limits and practical restrictions on materials and electrodes for miniaturization of cylindrical Hall thrusters (CHT). Analysis of the scaling relationships for plasma properties and thruster performance were derived and the thruster design, including the magnetic circuit, will be presented.
Waaaay too low thrust to be useful. Those kinds of engines work best in space for long-range missions, where their ability to keep low but constant acceleration for long periods of time means you can reach high velocities with little fuel. But for takeoff and landing, you need high thrust, because you're fighting gravity - hence chemical rockets.
Just did a bit of stubby pencil work. Ignoring fuel and power supply mass, a modern 30kw hall thruster strapped to Voyager 2 and run continuously until today would have accelerated the vehicle to 7 million mph (.01c)
This would place the vehicle at around 1.2 trillion miles away from us (.2ly).
Note that New Horizons has only 288 W and the Voyager probes had 480 W, so this really isn't a self-consistent scenario. (Solar power is much weaker still at those distances.)
The power requirements are very large for electric propulsion. It would be hard to generate enough electricity to have a good power to weight ratio. For a engine with similar thrust to the Falcon 9, you need ~186 gigawatts of electrical power (a significant portion of the US power grid). To generate that much power, you need a rocket engine, which defeats the purpose of going electric.
The main advantage of them is that you can run them for a year or two before they develop issues and they use much less propellant. Typically they are used as station keeping thrusters, where you don't care about the low thrust they generate.
[1]: https://www.dropbox.com/s/qd97lsm5iw3cvt3/CHT_Paper_Kennedy....
Abstract: Electric propulsion provides a significantly higher specific impulse that allows mass reduction for spacecraft when used in lieu of chemical propulsion. For micro and nano satellite applications, plasma thrusters should not only be miniaturized in mass and volume, but also capable of operating efficiently at very low power levels of a few watts or less. Research was conducted to determine theoretical limits and practical restrictions on materials and electrodes for miniaturization of cylindrical Hall thrusters (CHT). Analysis of the scaling relationships for plasma properties and thruster performance were derived and the thruster design, including the magnetic circuit, will be presented.