A resistive humidifier is literally a simple atmospheric (non-pressurized) boiler which simply uses a stainless steel barrel to boil the water to create steam. The advantage of this type of humidifier is that you modulate the heat to precisely modulate the output. Additionally, you can trickle in the water so the downtime compared to a canister is greatly reduced in terms of killing the boil and wasting water. Water quality is not as much as a concern when compared to canisters.
For the ultimate of precision, you can use Di-Ionized (DI) or Reverse Osmosis (RO) conditioned water which means the humidifier chamber never gets scale or needs any real cleaning.
Similar to canisters, it is non-pressurized steam, so the piping and pitch between the generator and distributer is important.
While it can be viewed as an advantage or a disadvantage, the fact remains that the resistive humidifier does not require canister replacement, which is equivalent to a few hundred $ per season. If you are using potable water, it will need to be cleaned regularly. Resistive humidifiers do have a higher first cost when compared to canisters.