I had a B12 deficiency and was told I couldn't absorb it. The shots did almost nothing so I started taking the methyl B12. It has made all the difference in the world, my level shot up to over 1000.
When I saw how high it was I slacked off on taking it, I maybe took it a few times a month. When my levels were tested again, I had dropped all the way down to 400 within a year. I'm trying to take it more consistently now, although I have a horrible memory and sometimes forget.

The last time it was tested about two years ago, it was back up to 1000. I'm getting it tested again this week, hopefully my forgetfulness hasn't caused it to drop again.