well, here's my own opinion....
AIRBRUSH:
ADVANTAGE - control airflow and paints, need a lot of patience to master it...
DISADVANTAGE - VERY COSTLY - don't ask, you know why....
SPRAY CAN:
ADVANTAGE - cheap - no need electricity nor compressor. practice makes perfect...
DISADVANTAGE - need proper timing - can spoile your day - or you might throw your kit for disappointment result...
GUNDAM PENS:
ADVANTAGE - just do the marking you need to details... if you don't do painting.... its okay.
DISADVANTAGE - kits so dull, no tense or whatever - just a plastic normal kit.... other spray it with a top coat.
HAND BRUSH:
ADVANTAGE - no electricity needed, just do it yourself -requires skill and mastery. same as airbrushing...
DISADVATAGE - hmmmm, takes you a long time to finished the kit... i usually paint small figures like warhammers... this one is huge man, i don't know i havent tried it....