By recalling Duda, the Mets avoid burning his final option year. Duda had just one option year left, but he was originally optioned to Vegas on August 5. Since he spent fewer than twenty days in the minors, the option doesn't count against his limit. Assuming the Mets keep Duda on the roster through the end of the season—a fair assumption on August 24—they'll be able to send him back and forth between the big leagues and minor leagues next year if they so desire.
In terms of performance, Duda was one of the Mets' best hitters this year before he hit the disabled list. He hit .235/.353/.438 in 269 plate appearances, which translates to a .347 wOBA and 124 wRC+. Among Mets hitters with at least 100 plate appearances, that puts Duda behind only David Wright, Josh Satin, and Marlon Byrd. The problem was his defense in the outfield and the presence of Ike Davis at first base, the position for which Duda is best suited. It'll be interesting to see how the Mets use him over the next few weeks.
As for Baxter, he's put up just a .282 wOBA and 79 wRC+ in 120 plate appearances in the big leagues this year. He's spent more time in Las Vegas, where he's hit very well. He'll very likely be back shortly after rosters expand in September.