Terrible signing. Too many years and too much money for a DH with no power.
The Royals were smart to buy out Butler's contract, he's been in a steady decline since 2012:
2012: .313 AVG, .373 OBP, .510 SLG, 29 HR
2013: .289 AVG, .374 OBP, .412 SLG, 15 HR
2014: .271 AVG, .323 OBP, .379 SLG, 9 HR
I'd be very surprised if he put up the same numbers he did last season... I think his line in 2015 will more likely be .255/.305/.350 with 6-8 home runs and before his contract is up the A's will be paying a majority of his salary for him to play somewhere else (if they can find someone willing to take him off their hands.)
Just to put this into perspective, $10M is what Jim Johnson got as a sub-3.00 ERA, 50 save closer last season... That obviously didn't work out, but that was the expectation. This season, $10M is getting a DH with Coco Crisp power that they'll be stuck with for two more years, each one likely being worse than the last.