Marte has had a very streaky season so far, but his overall record contains a ton of positive indicators. He's reduced his K:BB ratio from about 4.5/1 in Class AA last year to 3.4/1 at Indianapolis this season. His power, which emerged rather suddenly last season, continues to develop. And he continues to hit for a high average. His most recent month of numbers is excellent, but forget about that and look at the entire body of work. For a 23-year-old in Class AAA, there's very little not to like.
The numbers strongly suggest that Marte is ready for a promotion. That's the important thing. Beyond that, the timing is perfect. Nobody, certainly not starters Jose Tabata and Alex Presley, has really earned regular playing time in the corner outfield spots. The Pirates are very much in contention in the N.L. Central, and it's four weeks before the trading deadline. If Marte comes up now and hits well, the Pirates know that much more about themselves, and if they're still in contention, they can prioritize an upgrade at some other position.