You pointed to a predictive metric as a reason why though. You could have just said "I don't like it."
I don't like it because I think his ERA is deceptive and makes him appear to be a better pitcher than he actually is. I think if his ERA were 4.50, which I expect it to trend towards because SIERA does tend to predict future ERA (note that it predicts future ERA, not precisely what each plate appearance from here on out will be like), we would probably be unhappy with Davey Johnson putting him in at that point with many fresher options available in the bullpen.