Keith Law has him as the 37th best FA, writing:
"Yoon wasn't the same after the 2013 World Baseball Classic, returning to KBO late in the spring and eventually landing in the bullpen when he couldn't regain his stuff as a starter. Prior to 2013, Yoon would work in the 90-92 mph range in the rotation with a full assortment of off-speed pitches, including an above-average or better changeup.
In 2013, he dropped to 87-90 mph and had to rely even more on his secondary stuff, only getting his velocity back in relief work. His fastball is true and up in the zone, so it's more likely he ends up in relief here than in a rotation, but I'd at least give him a chance to show he can miss enough bats with the changeup and slider to end up a fourth or fifth fourth starter."