You know Vizcaino is only 24 years old right? Sure he can crash and bust, though he has electric stuff and we've seen pitchers who have failed as starters have success in the pen. You own one of those examples. As well, your be all and end all Steamer projects him to have a 3.27 ERA with a 10.05 K/9. I'm sure he'll rack up some holds if he's not closing in Atlanta's pen, so there is value with those peripherals.
Jeffress has actually been solid out of the Brewers pen since last year. I was shocked to see the statistics, since he was a mess in Toronto. Since last July, he's posted a 2.91 xFIP in 70.1 innings. He's overtaken Broxton as the main 8th inning guy now, so if he continues to rack up holds and post solid peripherals as he has been doing, he's a nice arm to have.