I had weekly injections for over a year. These were hydroxocobalamin 1000mcg injections. They did what they had to do, in that they kept the serum level > 1000.

I then stopped them to get a complete baseline reading, and it had dropped to 375 ng/L. Given the hassle of the injections, I now switched to the methyl 5000mcg B12/empty stomach routine. I will get a reading in a couple of weeks, but I have a hunch it works as well as - if not better than - the injections.

Best way to know for you personally is to have the B12 serum levels checked (and get a copy of the results). If the result is > 1000 after a longer period of taking the oral version, I see no benefit to switching to the injections. (especially not the cyano ones)