Seconded. There are a lot of clever ideas that I haven't seen anywhere in other probability books: A_p distributions, group invariance, the derivation of an ignorance prior as a multi-agents problem, etc.
The only lacking (due to obsolescence) chapter is the one about quantum mechanics. Jaynes advocates (although implicitly) a hidden variables theory, but so far Bell's and Kochen-Specher's theorems imposed heavy constraints on those.
You seem to imply that Jaynes was writing before Bell. That is not true by many decades. I suppose it is possible that the chapter is based on a paper he wrote before Bell, but he had half a century to revise it.
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