Most commercial products say to take with food.

B12 is not well absorbed orally however, and with food just about ruins its tiny benefit.
lipoic acid also shows in studies decreased absorption (the racemic mixture that is).

But other vitamins can be taken with food.

Products with B12 in them therefore should be taken on an empty stomach, if you want the benefits. (Studies have shown this true with RX drugs too, that come in microgram doses--thyroid hormone, and digoxin are examples).

When one sees this glaring error on labels of B12, that is a sign that the makers are not scientists, or do not read the literature on what they are selling.

So the Amazon reviews may reflect the fact that many are following label directions and would explain why for some there is no benefit. Those with CMT won't benefit much except for other body functions (not the nerve damage). Research into CMT has not yet found a supplement benefit yet. The hopeful Vit C issue about 10 yrs ago looked promising in animal models, but it fizzled in humans.