This is a shell game. There are literally hundreds of places that we would need to inspect in North Korea. Being allowed to make a quick visit to one site that we used to have full time access to is not a net gain for our side.
North Korea's nuclear program is a long term project of almost unparalleled secrecy. In the year that we've been gone, and the decade before that, any number of underground facilities could have been tapped to support this effort. We will be able to superficially check the current state of affairs at Yongbyon, but this won't tell us much that we don't already know.
I am not impressed. I'd caution anyone against being overly excited about this.