idk about b12. never touched the stuff. but remember that most gear will be oil based, so practicing with somethign like bacteriostatic water won't be the same. you'll have to push the plunger slower, etc. i think b12 is thinner, but idk

idk that i'd waste my money on b12, but to each his own.

do something easy your first time. hot shower, quad, stretch the skin out with one hand and pin with the other. it'll be a good first one b'c stretching the skin out makes it go in easier imho. and it'll be easier to aspirate with both hands.