I'm just here to put in my empirical two cents' worth: the healing isn't instant, and it is a crazy ride, but I'm finding it worthwhile. I'm definitely different, and better, than I was 2 and a half months ago, when I started this. One of the most obvious ways I noticed this was that, recently, in an airport and a mall, when I thought about putting more speed in my walk I HAD it to put on. Impossible a few months ago. Also, just being in the airport or the mall, even briefly, without severe crashing afterward (tiredness, yes, but we all know that's different from crashing) was pretty amazing. And I am now able to read more than a few pages at a time.
Even in the worst of past startup reaction, I could notice things that were getting better, which had not gotten better under any other protocol. Something that I noticed even in my November and December of Hell (all crash, all the time) was that the peripheral neuropathies were still getting better, although the rest of me was unspeakable.
But. It is not an instant cure: Freddd is right when he says that there are many corners to turn. While I have pulled out of being constantly crashy, things continue to be a bit crazy: I still have to exercise in careful little bits, I have (lighter-quality) brainfog off and on, orthostatic intolerance, weird mood episodes (luckily I've had good training for those during the rest of my life : ) ). Maybe, like Freddd, my ignorance is bliss, and that's why I keep on, complaining and whining about the upheavals, but not letting them knock me off my course. It helps that there's an intuitive feeling that it's right: whenever I take the active B12s, it feels as if my cells are waking up, and while that doesn't always feel good, it does feel more alive. I just added selenium to my protocol, as well as going from 3mg to 4mg of mb12/day, and one or both of those things has knocked me on my behind pretty good. Yet certain basic things just feel better, which is what keeps me going on. I don't have the money to take the tests, so for me all that is a moot point: I'm just doing my best to adhere to this protocol for 6 months, then I'll reassess (and I already know I'll have more brainpower to reassess with).
In my own case I feel I have nothing to lose by forging on regardless, because while many of the things I've tried in the past have helped some, or helped temporarily, I have still dropped into the pit afterwards, in a discouraging reversal of everything I'd gained and then some. Unlike many of you, I don't seem to have the sensitivities to fillers or environmental pollutants, though I've always tried to keep those down. I also don't have underlying thyroid problems, (one of the few things I did test for) though it makes sense to me that B12 deficiency would lead to adrenal deficiency which in turn would lead to thyroid deficieincy. (Originally I thought I had adrenal depletion and took Standard Process hormone-free glandulars for both adrenals and thyroid. This helped, but only to a certain point, so my empirical experience backs up the idea that the B12 deficiencies are (in my own case) the upstream cause of endocrine system problems. If I'd already had an endocrine system problem, that would have muddied the waters a bit. In my own case it was clear that the thyroid and adrenal support wasn't getting to the bottom of the problem.)
Basically, this protocol is the best alternative I've found. It's the only one where I've found talk about recovery or cure, as opposed to management and mitigation. And that is why I believe it's worth suffering through the nausea, brainfog, weird little electric dirls, exacerbated nerve pain, orthostatic intolerance, wacky moods, odd internal twitches, and the whole jolly crew of symptoms: it offers me the best possibility for getting a life. (I can already see it will not be "getting my life back", but I can work with that to make it a good thing. I often wonder if some of the anxiety about the B12 startup weirdness doesn't come from a sense that we are turning into different people. We are, but we have some say in how that happens and what we turn into. It could be a good thing.)