Dr. Garwin and Dr. Holt were the main organizers behind the group that wrote and signed the letter, according to two of the letter’s signatories.

These are the people who've advised Congress and presidents over the years on this issue. Their contribution to this discussion, as I noted, is to speak mostly from the science view, not necessarily the political one:

The body of the letter praises the technical features of the Iran accord and offers tacit rebuttals to recent criticisms on such issues as verification and provisions for investigating what specialists see as evidence of Iran’s past research on nuclear arms.

It also focuses on whether Iran could use the accord as diplomatic cover to pursue nuclear weapons in secret.

The deal’s plan for resolving disputes, the letter says, greatly mitigates “concerns about clandestine activities.” It hails the 24-day cap on Iranian delays to site investigations as “unprecedented,” adding that the agreement “will allow effective challenge inspection for the suspected activities of greatest concern.”

If you've found that what they've written is not correct, post the link. If you want to wig off to why the agreement didn't include return of Americans in Iran or something to do with funding radical groups outside Iran, I'll only point out that is not what it's about.