Well, I thought (assumed) that MSG caused raised blood pressure like salt would [salt acts immediately I gather, I thought it was the sodium??], but according to the this HN thread there are no adverse reactions other than extremely rare allergies?

https://pubmed.ncbi.nlm.nih.gov/21372742/ (first paper SERPs returned for me) suggests that MSG increases BP over the order of years. Not sure the "it's entirely healthy" claims pan out?

Yeah, the sodium part can definitely be a problem for some people, although for healthy people sodium won't actually make blood pressure go up.