b12 orally has poor bioavailability, best bet is to inject it, its safe, as far as i remember helps increase your Red Blood Cell count. main reason I started doing it since last year was for appetite increases.
And yeh, it does work, i haven't injected for about a month to give my body a break, but it worked wonders for appetite when i took my first few injections, twice or once per week are fine...
Lowers Homocysteine too, which helps increase N.O. if i remember correctly...
As for the vitamin C, yeh you can inject that if you wana, dont see the point though, but if you did you would need Sodium Ascorbate or something similar instead of just Ascorbic Acid (straight vitamin c) because it will be too acidic otherwise. Oh, and b12, it will help increase energy for sure too