From Pierre LeBrun:

Great landing spot for Simmonds, who goes to a contender in the Western Conference. Nashville is second in the central division on 77 points, just one point behind Winnipeg. Simmer will reunite with Peter Laviolette, having played under Lavy from 2011-2014 in Philadelphia.

Bob McKenzie has more on the trade details:

Nashville should win a round in the playoffs, so I think the Flyers are probably getting a third out of this.

As for Hartman, he was trade to Nashville from Chicago last season, a 24-year-old third-line right winger with 10 goals and 10 assists this year. He looks to be a restricted free agent at season’s end. 

So that’s… not really much of a return for Simmonds, a bottom-6 guy and a conditional fourth-rounder. But at this point in his career, Simmer is a 30-year-old 3rd line unrestricted free agent, so I guess the glass-half-full approach is to be happy for getting anything at all for a guy on an expiring contract. The glass-half-empty approach is to think that Chuck Fletcher held his cards too long.