I'm no chemist, so don't fully understand the links, but it seems that monosodium glutamate and umami are closely associated. Some people might view that as a bad thing, though I do not.

Sorry, michaelr, no Waitrose near me, so I can't help your research at this time. If the product starts to get a wider distribution I may be able to try it in due course. I'll keep my eye out for it.