Have to agree that MTHFR is surrounded by some of the most obnoxious quackery. I feel like it has been promoted as some ultimate cure. I do think the concern is legit, but would definitely steer away from quacks selling ebooks and their own supplements.

Supplementing folate and B12 won't have any earth-shattering overnight effects.

From my experience supplemental b-vitamins can actually have a huge impact on your mood for an undefined period of time when you start them. It could be a small effect that get amplified by additional placebo and blown out of proportion though, least in my case.

Personally I have tested myself and appear to be homozygous for C677T [rs1801133(T;T)]. I also have Two copies of GCH1 variant (gs224) associated with lower levels of tetrahydrobiopterin and rs5030853(G;G). rs5030853 has been linked to BH4 responsiveness and developing phenylketonuria.

Should probably get tested for mild hyperphenylalaninemia.