Injectable isn't much better. B12 is absorbed pretty well and excreted pretty quickly. You can get sublinqual with folic acid and it'll work just as well.
Oral B12 from what I have read from more sources than not is absorbed very poorly. It does not do alot but it is beneficial. I oreder mine from a Canadian pharmacy. $10 for each 10ml vial and it is made by Sandoz, a Swiss pharmacology company that gained fame in the 50's for it's synthesis of LSD-25 after Albert Hoffman collaborated with them. Quality stuff and cheap for human grade.