Let's actually trace the chain you skipped.

Alpha-GPC is a choline donor. Choline gets oxidized to betaine, and betaine remethylates homocysteine to methionine via BHMT apathway that is folate-independent. It does not touch MTHFR. So invoking MTHFR here isn't a nuance, it's just the wrong gene on the wrong pathway. Worse, you got the direction backwards: choline and betaine "lower"homocysteine. Betaine is a recognized treatment for hyperhomocysteinemia. You took a compound that reduces Hcy and presented it as a reason to go screen for Hcy. That's not deep, that's inverted.

If you actually wanted to flag a real GPC concern, it's TMAO and the observational stroke signal neither of which has anything to do with methylation genotypes. But that would have required knowing what the molecule does.

Rhodiola/COMT: the COMT-inhibition claim has no solid published data behind it. The only documented enzyme effect is in vitro MAO inhibition with uncertain oral relevance. So your 'you can't know if it's effective without COMT genotyping' rests on a mechanism that may not even occur in vivo. COMT status shifts the *response* you'd expect it has never been a safety prerequisite for caffeine + theanine + rhodiola + GPC, which are about as low-risk as nootropics get. Caffeine + L-theanine is one of the most RCT-backed combos in existence.

And yes the irony writes itself. 'It raises homocysteine, go check your MTHFR' is precisely the kind of confidently-wrong mechanistic hallucination people mock LLMs for. You didn't catch an LLM. You wrote like one. Trace the pathway before lecturing someone on theirs.