Problems, problems, problems. Nothing but problems.
Due to the typical black box approach to TRNG production, nothing can be audited, tested nor taken for granted. TRNG consumers simply have to rely on social trust in the commercial manufacturer. As the saying goes, nobody ever got fired for buying IBM. But then, you could verify that an IBM mainframe was behaving as the glossy sales brochure said it would.
That’s just not the case with an encapsulated TRNG and it’s specification sheet. There may be an (un)intentional variance between the two. When the elusiveness of Truth is taken in aggregate with the impossibility of TRNG audit and conspiratorial indeterminacy, you realise why you should build your own.