Easy to clean. At the sink with hot water.
Unscrew the knurled ring from the bottom. Pull it off the tank and set in sink.
Fill tank with hot water, shake, dump. Repeat as needed.
Set aside for drying.
Pick up bottom piece and wiggle the white silicone rubber piece off, rinse under running water and set aside to dry.
Unscrew the remaining piece - the actual head assembly - from the bottom piece. At this point, you can choose to toss it and use a new one, or clean it. More running water, only pat dry, don't wipe! You'll ruin the wicks.
Once all's dry - patience, or a hair dryer, or even just "mostly" dry

- screw the head (or new one) into the base. Put the rubber piece on, fill tube and put the base on.
Heads do come in different resistances, tiny numbers etched on the head, so you can't see it unless it's all taken apart. Once you find the value that works for you, just buy that value spares.
Plug one, maybe two, of the tiny holes in the base. Work the tip of a toothpick in. Changes the draw. Or you could try an Evod head. Some say it tightens the draw, but I've not tried it. Yet
