There is another issue people seem to be unaware of, which is that the body cannot utilise B12 in its normal, water soluble, form, but must first metabolise it to a lipid soluble form which can be absorbed by the tissues.
In some people, this conversion doesn't work so well, so even if your levels of B12 are measured as "normal", it may be that you can't actually use it.
I think I have this problem so I take my B12 as its methyl form (Aka Methyl Cobolamine) and, in conjunction with alpha Lipoic Acid I find it helps with my Neuropathy problems, and also with my FBG levels.
I'm type 2, diagnosed July 2014 and taking 3 x 500mg Metformin daily. I was taking 4, but after adding the supplements I found 3 to work fine. Going down to 2 though seemed to be sending them the wrong way....