The Falcons have Jake Matthews and Ryan Schraeder available at tackle, but beyond those two they have players who are either injured or have a track record of mixed success. The team is cognizant of that weakness.
Long is the kind of player we'd all get hyped for if this workout was taking place in 2013, even, but he's not the same caliber of player he was when he was selected in the top ten back in 2008. After his second career ACL tear in 2014, a season that saw him play just seven games, there was little interest on the open market for his services.
Long is a better athlete and thus a better scheme fit for Atlanta than Gosder Cherilus, the other once heralded 2008 tackle who is on the open market, so a signing would make real sense for the Falcons. The question is whether Long's recuperated to the point where he can be an asset for the team, and whether he's even 75% of the player he once was. It's worth a short-term deal to find out, but Long's slow decline and the devastating nature of ACL injuries for a 30-year-old offensive tackle means you should keep your expectations low.
Hopefully, though, Long winds up in Atlanta, returns to form and gives the team a reasonably formidable set of tackles in 2015. A man can dream.