I think the boost is placebo mostly. I did some b-vitamin shots, a painful 3ml amp, didn't notice shit.
As far as b12, well, the oral is absorbed, not quite as well as injectable but the research is there if you want to have a look. Go to pubmed and search for injectable vs oral b12. If I wanted b12 I would take oral methylcobalamin. There are 1, 2, 5 and even 15mg tablets/lozenges of of this stuff. Very very high dose, like a million percent of daily recommendation, so you will be swimming in b12 for sure, relatively poor oral absorption or not.
I would like some injectable glutathione though.