Burns is a decent little prospect but he's 24, he hits for no power, & the Nats have a few decent OF prospects. Might be what, 15th next year in Nats prospects?
Blevins is a good LH reliever. I'll bring up splits tomorrow but pitched well vs righties in his career. He was specifically good in 2013. (and specificallly not so good versus left-handed batters). All in all better versus lefties in career though as you'd expect.
It's a good deal for a Nats team that wants to win in 2014 not wait around and see if Billy Burns might be a cheap 3rd-4th OF for 2016-2020.