Between 2015 and 2017, the cumulative WAR leaders among relievers are Jansen, Miller, Chapman, Betances, Osuna, Kimbrel, Giles, Britton, Allen, and Robertson.
Those 10 guys reordered via xFIP are Miller, Jansen, Britton, Kimbrel, Chapman, Betances, Giles, Robertson, Allen, Osuna.
Basically we got a guy who is effectively an equal to Osuna plus two prospects, in exchange for losing a year of control. I would have preferred to get an elite prospect instead of a closer back, but value wise this was just fine.